Heterocyclic compound, light-emitting element, light-emitting device, electronic device, and lighting device

ABSTRACT

An object is to provide a novel heterocyclic compound which can be used for a light-emitting element, as a host material of a light-emitting layer in which a light-emitting substance is dispersed. Other objects are to provide a light-emitting element having low driving voltage, a light-emitting element having high current efficiency, and a light-emitting element having a long lifetime. Provided are a light-emitting element including a compound in which a dibenzo[f,h]quinoxaline ring and a hole-transport skeleton are bonded through an arylene group, and a light-emitting device, an electronic device, and a lighting device each using this light-emitting element. The heterocyclic compound represented by General Formula (G1) below is provided.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.13/031,734, filed Feb. 22, 2011, now allowed, which claims the benefitof foreign a priority application filed in Japan as Serial No.2010-044720 on Mar. 1, 2010, both of which are incorporated byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a heterocyclic compound, alight-emitting element, a light-emitting device, an electronic device,and a lighting device.

2. Description of the Related Art

In recent years, research and development have been extensivelyconducted on light-emitting elements utilizing electroluminescence (EL).In the basic structure of such a light-emitting element, a layercontaining a light-emitting substance is interposed between a pair ofelectrodes. By voltage application to this element, light emission fromthe light-emitting substance can be obtained.

Since such light-emitting elements are self-luminous elements, they haveadvantages over liquid crystal displays in having high pixel visibilityand eliminating the need for backlights, for example, thereby beingconsidered as suitable for flat panel display elements. Light-emittingelements are also highly advantageous in that they can be thin andlightweight. Furthermore, very high speed response is one of thefeatures of such elements.

Furthermore, since such light-emitting elements can be formed in a filmform, they make it possible to provide planar light emission.Accordingly, elements having a large area can be easily formed. This isa feature difficult to obtain with point light sources typified byincandescent lamps and LEDs or linear light sources typified byfluorescent lamps. Thus, light-emitting elements also have greatpotential as planar light sources applicable to lightings and the like.

Such light-emitting elements utilizing electroluminescence can bebroadly classified according to whether a light-emitting substance is anorganic compound or an inorganic compound. In the case of an organic ELelement in which a layer containing an organic compound used as alight-emitting substance is provided between a pair of electrodes,application of a voltage to the light-emitting element causes injectionof electrons from a cathode and holes from an anode into the layercontaining the organic compound having a light-emitting property andthus a current flows. The injected electrons and holes then lead theorganic compound having a light-emitting property to its excited state,whereby light emission is obtained from the excited organic compoundhaving a light-emitting property.

The excited state formed by an organic compound can be a singlet excitedstate or a triplet excited state. Emission from the singlet excitedstate (S*) is called fluorescence, and emission from the triplet excitedstate (T*) is called phosphorescence. In addition, the statisticalgeneration ratio thereof in a light-emitting element is considered to beas follows: S*:T*=1:3.

In a compound which converts energy of a singlet excited state intolight emission (hereinafter, referred to as a fluorescent compound), atroom temperature, emission from the triplet excited state(phosphorescence) is not observed while only emission from the singletexcited state (fluorescence) is observed. Therefore the internal quantumefficiency (the ratio of generated photons to injected carriers) of alight-emitting element using a fluorescent compound is assumed to have atheoretical limit of 25% based on the ratio of S* to T* which is 1:3.

In contrast, in a compound which converts energy of a triplet excitedstate into light emission (hereinafter, referred to as a phosphorescentcompound), emission from the triplet excited state (phosphorescence) isobserved. Further, in a phosphorescent compound, since intersystemcrossing (i.e. transfer from a singlet excited state to a tripletexcited state) easily occurs, the internal quantum efficiency can beincreased to 75% to 100% in theory. In other words, the emissionefficiency can be three to four times as much as that of a fluorescentcompound. For this reason, light-emitting elements using phosphorescentcompounds are now under active development in order to realize highlyefficient light-emitting elements.

When a light-emitting layer of a light-emitting element is formed usinga phosphorescent compound described above, in order to suppressconcentration quenching or quenching due to triplet-triplet annihilationin the phosphorescent compound, the light-emitting layer is often formedsuch that the phosphorescent compound is dispersed in a matrix ofanother compound. Here, the compound serving as the matrix is called ahost material, and the compound dispersed in the matrix, such as aphosphorescent compound, is called a guest material.

In the case where a phosphorescent compound is a guest material, a hostmaterial needs to have higher triplet excitation energy (a larger energydifference between a ground state and a triplet excited state) than thephosphorescent compound.

Furthermore, since singlet excitation energy (an energy differencebetween a ground state and a singlet excited state) is higher thantriplet excitation energy, a substance that has high triplet excitationenergy also has high singlet excitation energy. Therefore the abovesubstance that has high triplet excitation energy is also effective in alight-emitting element using a fluorescent compound as a light-emittingsubstance.

Studies have been conducted on compounds having dibenzo[f,h]quinoxalinerings, which are examples of the host material used when aphosphorescent compound is a guest material (e.g., see Patent Documents1 and 2).

REFERENCES

-   Patent Document 1: PCT International Publication No. 03/058667-   Patent Document 2: Japanese Published Patent Application No.    2007-189001

SUMMARY OF THE INVENTION

However, the above compounds having dibenzo[f,h]quinoxaline rings have aplanar structure, and accordingly, these compounds are easilycrystallized. A light-emitting element using a compound that is easy tocrystallize has a short lifetime. Further, if another skeleton isdirectly bonded to the dibenzo[f,h]quinoxaline ring so that the compoundhas a three-dimensionally bulky structure, the conjugated system couldpossibly extend to cause a decrease in triplet excitation energy.

Further, in order to realize a light-emitting device, an electronicdevice, and a lighting device each having reduced power consumption andhigh reliability, a light-emitting element having low driving voltage, alight-emitting element having high current efficiency, or alight-emitting element having a long lifetime have been expected.

Therefore an object of one embodiment of the present invention is toprovide a novel heterocyclic compound which can be used for alight-emitting element, as a host material of a light-emitting layer inwhich a light-emitting substance is dispersed, in particular, a novelheterocyclic compound which can be suitably used as a host material inwhich a phosphorescent compound is used as a light-emitting substance.

Another object of one embodiment of the present invention is to providea light-emitting element having low driving voltage. Yet another objectof one embodiment of the present invention is to provide alight-emitting element having high current efficiency. Another object ofone embodiment of the present invention is to provide a light-emittingelement having a long lifetime. Still another object of one embodimentof the present invention is to provide a light-emitting device, anelectronic device, and a lighting device each having reduced powerconsumption by use of any of these light-emitting elements.

A compound with a quinoxaline skeleton has a high electron-transportproperty, and use of such a compound for a light-emitting elementenables the element to have low driving voltage. However, a quinoxalineskeleton has a planar structure. Since a compound having a planarstructure is easily crystallized when formed into a film, use of such acompound for light-emitting elements causes the elements to have a shorta lifetime. Furthermore, a quinoxaline skeleton is poor at acceptingholes. When a compound that cannot easily accept holes is used as a hostmaterial of a light-emitting layer, the region of electron-holerecombination concentrates on an interface of the light-emitting layer,leading to a reduction in the lifetime of the light-emitting element. Itis likely that these problems will be solved by introduction of ahole-transport skeleton into the molecule. However, if a hole-transportskeleton is directly bonded to a quinoxaline skeleton, the conjugatedsystem extends to cause a decrease in band gap and a decrease in tripletexcitation energy.

Nevertheless, the present inventors have found that the above problemscan be solved by using, for a light-emitting element, a compound inwhich a dibenzo[f,h]quinoxaline ring and a hole-transport skeleton arebonded through an arylene group.

One embodiment of the present invention is a light-emitting elementincluding a compound in which a dibenzo[f,h]quinoxaline ring and ahole-transport skeleton are bonded through an arylene group.

A compound applied to one embodiment of the present invention has ahole-transport skeleton in addition to a dibenzo[f,h]quinoxaline ring,making it easy to accept holes. Accordingly, by use of the compound as ahost material of a light-emitting layer, electrons and holes recombinein the light-emitting layer, so that it is possible to suppress thedecrease in the lifetime of the light-emitting element. Furthermore, theintroduction of a hole-transport skeleton enables the compound to have athree-dimensionally bulky structure, and the compound is difficult tocrystallize when formed into a film. By the use of the compound for alight-emitting element, the element can have a long lifetime. Moreover,in this compound, since a dibenzo[f,h]quinoxaline ring and ahole-transport skeleton are bonded through an arylene group, decreasesin band gap and triplet excitation energy can be prevented as comparedwith a compound in which a dibenzo[f,h]quinoxaline ring and ahole-transport skeleton are directly bonded. By the use of the compoundfor a light-emitting element, the element can have high currentefficiency.

Thus, the compound described above can be suitably used as a materialfor an organic device such as a light-emitting element or an organictransistor.

As the hole-transport skeleton, a π-electron rich heteroaromatic ring ispreferable. As the π-electron rich heteroaromatic ring, a carbazolering, a dibenzofuran ring, or a dibenzothiophene ring is preferable. Asthe arylene group, any of a substituted or unsubstituted phenylene groupand a substituted or unsubstituted biphenyldiyl group is preferable.

Since a light-emitting element of one embodiment of the presentinvention which is obtained as above has low driving voltage, highcurrent efficiency, and a long lifetime, a light-emitting device (suchas an image display device) using this light-emitting element can havereduced power consumption. Thus, one embodiment of the present inventionis a light-emitting device including any of the above light-emittingelements. One embodiment of the present invention also includes anelectronic device using the light-emitting device in its display portionand a lighting device using the light-emitting device in itslight-emitting portion.

The light-emitting device in this specification covers an image displaydevice using a light-emitting element and also the following devices: amodule including a light-emitting element to which a connector such asan anisotropic conductive film, a TAB (tape automated bonding) tape, ora TCP (tape carrier package) is attached; a module in which the top of aTAB tape or a TCP is provided with a printed wiring board; a module inwhich an IC (integrated circuit) is directly mounted on a light-emittingelement by a COG (chip on glass) technique; and further a light-emittingdevice used for a lighting device and the like.

As the compound in which a dibenzo[f,h]quinoxaline ring and ahole-transport skeleton are bonded through an arylene group, aheterocyclic compound below can be given.

One embodiment of the present invention is a heterocyclic compoundrepresented by General Formula (G1) below.

In General Formula (G1), A represents any of a substituted orunsubstituted carbazolyl group, a substituted or unsubstituteddibenzothiophenyl group, and a substituted or unsubstituteddibenzofuranyl group, R¹¹ to R¹⁹ separately represent any of hydrogen,an alkyl group having 1 to 4 carbon atoms, and a substituted orunsubstituted aryl group having 6 to 13 carbon atoms, and Ar representsan arylene group having 6 to 13 carbon atoms. The arylene group may haveone or more substituents, and the substituents may be bonded to form aring.

Another embodiment of the present invention is a heterocyclic compoundrepresented by General Formula (G2-1) below.

In General Formula (G2-1), Z represents oxygen or sulfur, R¹¹ to R¹⁹ andR²¹ to R²⁷ separately represent hydrogen, an alkyl group having 1 to 4carbon atoms, or a substituted or unsubstituted aryl group having 6 to13 carbon atoms, and Ar represents an arylene group having 6 to 13carbon atoms. The arylene group may have one or more substituents, andthe substituents may be bonded to form a ring.

Another embodiment of the present invention is a heterocyclic compoundrepresented by General Formula (G2-2) below.

In General Formula (G2-2), R¹¹ to R¹⁹ and R³¹ to R³⁸ separatelyrepresent hydrogen, an alkyl group having 1 to 4 carbon atoms, or asubstituted or unsubstituted aryl group having 6 to 13 carbon atoms, andAr represents an arylene group having 6 to 13 carbon atoms. The arylenegroup may have one or more substituents, and the substituents may bebonded to form a ring.

In General Formulae (G2-1) and (G2-2), Ar is preferably any of asubstituted or unsubstituted phenylene group and a substituted orunsubstituted biphenyldiyl group, particularly a substituted orunsubstituted phenylene group. Furthermore, Ar is much preferably asubstituted or unsubstituted m-phenylene group so as to have a hightriplet excited energy level (T1 level).

Another embodiment of the present invention is a heterocyclic compoundrepresented by General Formula (G3-1) below.

In General Formula (G3-1), Z represents oxygen or sulfur, R¹¹ to R¹⁹,R²¹ to R²⁷, and R⁴¹ to R⁴⁴ separately represent hydrogen, an alkyl grouphaving 1 to 4 carbon atoms, or a substituted or unsubstituted aryl grouphaving 6 to 13 carbon atoms.

Yet another embodiment of the present invention is a heterocycliccompound represented by General Formula (G3-2) below.

In General Formula (G3-2), R¹¹ to R¹⁹, R³¹ to R³⁸, and R⁴¹ to R⁴⁴separately represent hydrogen, an alkyl group having 1 to 4 carbonatoms, or a substituted or unsubstituted aryl group having 6 to 13carbon atoms.

The above heterocyclic compounds are also categorized as the alreadydescribed compound in which a dibenzo[f,h]quinoxaline ring and ahole-transport skeleton are bonded through an arylene group. Hence, oneembodiment of the present invention further covers a light-emittingelement including any of the above heterocyclic compounds. Also, oneembodiment of the present invention covers a light-emitting device, anelectronic device, and a lighting device each including thelight-emitting element.

One embodiment of the present invention can provide a novel heterocycliccompound which can be used for a light-emitting element, as a hostmaterial of a light-emitting layer in which a light-emitting substanceis dispersed. Another embodiment of the present invention can provide alight-emitting element having low driving voltage. Yet anotherembodiment of the present invention can provide a light-emitting elementhaving high current efficiency. Still another embodiment of the presentinvention can provide a light-emitting element having a long lifetime.By using the light-emitting element, another embodiment of the presentinvention can provide a light-emitting device, an electronic device, anda lighting device each having reduced power consumption.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B each illustrate a light-emitting element of oneembodiment of the present invention.

FIGS. 2A and 2B each illustrate a light-emitting element of oneembodiment of the present invention.

FIGS. 3A and 3B illustrate a light-emitting device of one embodiment ofthe present invention.

FIGS. 4A and 4B illustrate a light-emitting device of one embodiment ofthe present invention.

FIGS. 5A to 5D each illustrate an electronic device of one embodiment ofthe present invention.

FIG. 6 illustrates a liquid crystal display device of one embodiment ofthe present invention.

FIG. 7 illustrates a lighting device of one embodiment of the presentinvention.

FIG. 8 illustrates a lighting device of one embodiment of the presentinvention.

FIGS. 9A and 9B show ¹H NMR charts of2-[3-(dibenzothiophen-4-yl)phenyl]dibenzo[f,h]quinoxaline (abbreviation:2mDBTPDBq-II).

FIGS. 10A and 10B show respectively an absorption spectrum and anemission spectrum of a toluene solution of 2mDBTPDBq-II.

FIGS. 11A and 11B show respectively an absorption spectrum and anemission spectrum of a thin film of 2mDBTPDBq-II.

FIGS. 12A and 12B show ¹H NMR charts of2-[4-(3,6-diphenyl-9H-carbazol-9-yl)phenyl]dibenzo[f,h]quinoxaline(abbreviation: 2CzPDBq-III).

FIGS. 13A and 13B show respectively an absorption spectrum and anemission spectrum of a toluene solution of 2CzPDBq-III.

FIGS. 14A and 14B show respectively an absorption spectrum and anemission spectrum of a thin film of 2CzPDBq-III.

FIG. 15 shows voltage vs. luminance characteristics of light-emittingelements of Example 3.

FIG. 16 shows luminance vs. current efficiency characteristics of thelight-emitting elements of Example 3.

FIG. 17 shows results of reliability tests of the light-emittingelements of Example 3.

FIG. 18 illustrates a light-emitting element of Examples.

FIGS. 19A and 19B show ¹H NMR charts of2-[4-(dibenzothiophen-4-yl)phenyl]dibenzo[f,h]quinoxaline (abbreviation:2DBTPDBq-II).

FIGS. 20A and 20B show respectively an absorption spectrum and anemission spectrum of a toluene solution of 2DBTPDBq-II.

FIGS. 21A and 21B show respectively an absorption spectrum and anemission spectrum of a thin film of 2DBTPDBq-II.

FIGS. 22A and 22B show ¹H NMR charts of2-[3′-(dibenzothiophen-4-yl)biphenyl-3-yl]dibenzo[f,h]quinoxaline(abbreviation: 2mDBTBPDBq-II).

FIGS. 23A and 23B show respectively an absorption spectrum and anemission spectrum of a toluene solution of 2mDBTBPDBq-II.

FIGS. 24A and 24B show respectively an absorption spectrum and anemission spectrum of a thin film of 2mDBTBPDBq-II.

FIGS. 25A and 25B show ¹H NMR charts of2-[3-(2,8-diphenyldibenzothiophen-4-yl)phenyl]dibenzo[f,h]quinoxaline(abbreviation: 2mDBTPDBq-III).

FIGS. 26A and 26B show respectively an absorption spectrum and anemission spectrum of a toluene solution of 2mDBTPDBq-III.

FIGS. 27A and 27B show respectively an absorption spectrum and anemission spectrum of a thin film of 2mDBTPDBq-III.

FIGS. 28A and 28B show ¹H NMR charts of2-[3-(dibenzothiophen-4-yl)phenyl]-3-phenyldibenzo[f,h]quinoxaline(abbreviation: 3Ph-2mDBTPDBq-II).

FIGS. 29A and 29B show respectively an absorption spectrum and anemission spectrum of a toluene solution of 3Ph-2mDBTPDBq-II.

FIGS. 30A and 30B show respectively an absorption spectrum and anemission spectrum of a thin film of 3Ph-2mDBTPDBq-II.

FIGS. 31A and 31B show ¹H NMR charts of2-[3-(dibenzofuran-4-yl)phenyl]dibenzo[f,h]quinoxaline (abbreviation:2mDBFPDBq-II).

FIGS. 32A and 32B show respectively an absorption spectrum and anemission spectrum of a toluene solution of 2mDBFPDBq-II.

FIGS. 33A and 33B show respectively an absorption spectrum and anemission spectrum of a thin film of 2mDBFPDBq-II.

FIGS. 34A and 34B show ¹H NMR charts of2-[3′-(9H-carbazol-9-yl)biphenyl-3-yl]dibenzo[f,h]quinoxaline(abbreviation: 2mCzBPDBq).

FIGS. 35A and 35B show respectively an absorption spectrum and anemission spectrum of a toluene solution of 2mCzBPDBq.

FIGS. 36A and 36B show respectively an absorption spectrum and anemission spectrum of a thin film of 2mCzBPDBq.

FIGS. 37A and 37B show ¹H NMR charts of2-[3-(3,6-diphenyl-9H-carbazol-9-yl)phenyl]dibenzo[h]quinoxaline(abbreviation: 2mCzPDBq-III).

FIGS. 38A and 38B show respectively an absorption spectrum and anemission spectrum of a toluene solution of 2mCzPDBq-III.

FIGS. 39A and 39B show respectively an absorption spectrum and anemission spectrum of a thin film of 2mCzPDBq-III.

FIGS. 40A and 40B show ¹H NMR charts of2-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]dibenzo[f,h]quinoxaline(abbreviation: PCPDBq).

FIGS. 41A and 41B show respectively an absorption spectrum and anemission spectrum of a toluene solution of PCPDBq.

FIGS. 42A and 42B show respectively an absorption spectrum and anemission spectrum of a thin film of PCPDBq.

FIGS. 43A and 43B show ¹H NMR charts of2-[3-(dibenzothiophen-2-yl)phenyl]dibenzo[f,h]quinoxaline (abbreviation:2mDBTPDBq).

FIGS. 44A and 44B show respectively an absorption spectrum and anemission spectrum of a toluene solution of 2mDBTPDBq.

FIGS. 45A and 45B show respectively an absorption spectrum and anemission spectrum of a thin film of 2mDBTPDBq.

FIG. 46 shows voltage vs. luminance characteristics of a light-emittingelement of Example 13.

FIG. 47 shows luminance vs. current efficiency characteristics of thelight-emitting element of Example 13.

FIG. 48 shows results of reliability tests of the light-emitting elementof Example 13.

FIG. 49 shows voltage vs. luminance characteristics of a light-emittingelement of Example 14.

FIG. 50 shows luminance vs. current efficiency characteristics of thelight-emitting element of Example 14.

FIG. 51 shows results of reliability tests of the light-emitting elementof Example 14.

FIG. 52 shows voltage vs. luminance characteristics of a light-emittingelement of Example 15.

FIG. 53 shows luminance vs. current efficiency characteristics of thelight-emitting element of Example 15.

FIG. 54 shows voltage vs. luminance characteristics of a light-emittingelement of Example 16.

FIG. 55 shows luminance vs. current efficiency characteristics of thelight-emitting element of Example 16.

FIG. 56 shows voltage vs. luminance characteristics of a light-emittingelement of Example 17.

FIG. 57 shows luminance vs. current efficiency characteristics of thelight-emitting element of Example 17.

FIG. 58 shows voltage vs. luminance characteristics of a light-emittingelement of Example 18.

FIG. 59 shows luminance vs. current efficiency characteristics of thelight-emitting element of Example 18.

FIG. 60 shows voltage vs. luminance characteristics of a light-emittingelement of Example 19.

FIG. 61 shows luminance vs. current efficiency characteristics of thelight-emitting element of Example 19.

FIG. 62 shows voltage vs. luminance characteristics of a light-emittingelement of Example 20.

FIG. 63 shows luminance vs. current efficiency characteristics of thelight-emitting element of Example 20.

FIG. 64 shows current density vs. luminance characteristics oflight-emitting elements of Example 21.

FIG. 65 shows voltage vs. luminance characteristics of thelight-emitting elements of Example 21.

FIG. 66 shows luminance vs. current efficiency characteristics of thelight-emitting elements of Example 21.

FIG. 67 shows voltage vs. current characteristics of the light-emittingelements of Example 21.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the present invention will now be described withreference to the accompanying drawings. Note that the invention is notlimited to the description below, and it will be easily understood bythose skilled in the art that various changes and modifications can bemade without departing from the spirit and scope of the invention.Therefore, the invention should not be construed as being limited to thedescription in the following Embodiments.

Embodiment 1

In Embodiment 1, a heterocyclic compound of one embodiment of thepresent invention will be described.

One embodiment of the present invention is the heterocyclic compoundrepresented by General Formula (G1).

In General Formula (G1), A represents any of a substituted orunsubstituted carbazolyl group, a substituted or unsubstituteddibenzothiophenyl group, and a substituted or unsubstituteddibenzofuranyl group, R¹¹ to R¹⁹ separately represent any of hydrogen,an alkyl group having 1 to 4 carbon atoms, and a substituted orunsubstituted aryl group having 6 to 13 carbon atoms, and Ar representsan arylene group having 6 to 13 carbon atoms. The arylene group may haveone or more substituents, and the substituents may be bonded to form aring.

Another embodiment of the present invention is the heterocyclic compoundrepresented by General Formula (G2-1) below.

In General Formula (G2-1), Z represents oxygen or sulfur, R¹¹ to R¹⁹ andR²¹ to R²⁷ separately represent hydrogen, an alkyl group having 1 to 4carbon atoms, or a substituted or unsubstituted aryl group having 6 to13 carbon atoms, and Ar represents an arylene group having 6 to 13carbon atoms. The arylene group may have one or more substituents, andthe substituents may be bonded to form a ring.

Another embodiment of the present invention is the heterocyclic compoundrepresented by General Formula (G2-2) below.

In General Formula (G2-2), R¹¹ to R¹⁹ and R³¹ to R³⁸ separatelyrepresent hydrogen, an alkyl group having 1 to 4 carbon atoms, or asubstituted or unsubstituted aryl group having 6 to 13 carbon atoms, andAr represents an arylene group having 6 to 13 carbon atoms. The arylenegroup may have one or more substituents, and the substituents may bebonded to form a ring.

In General Formulae (G2-1) and (G2-2), Ar is preferably any of asubstituted or unsubstituted phenylene group and a substituted orunsubstituted biphenyldiyl group, particularly a substituted orunsubstituted phenylene group. Furthermore, Ar is much preferably asubstituted or unsubstituted m-phenylene group so as to have a hightriplet excited energy level (T1 level).

Another embodiment of the present invention is the heterocyclic compoundrepresented by General Formula (G3-1) below.

In General Formula (G3-1), Z represents oxygen or sulfur, R¹¹ to R¹⁹,R²¹ to R²⁷, and R⁴¹ to R⁴⁴ separately represent hydrogen, an alkyl grouphaving 1 to 4 carbon atoms, or a substituted or unsubstituted aryl grouphaving 6 to 13 carbon atoms.

Yet another embodiment of the present invention is the heterocycliccompound represented by General Formula (G3-2) below.

In General Formula (G3-2), R¹¹ to R¹⁹, R³¹ to R³⁸, and R⁴¹ to R⁴⁴separately represent hydrogen, an alkyl group having 1 to 4 carbonatoms, or a substituted or unsubstituted aryl group having 6 to 13carbon atoms.

Examples of the specific structures of Ar in General Formulae (G1),(G2-1), and (G2-2) include substituents represented by StructuralFormulae (1-1) to (1-15).

Examples of the specific structures of R¹¹ to R¹⁹, R²¹ to R²⁷, R³¹ toR³⁸, and R⁴¹ to R⁴⁴ in General Formulae (G1), (G2-1), (G2-2), (G3-1),and (G3-2) include substituents represented by Structural Formulae (2-1)to (2-23).

Specific examples of the heterocyclic compound represented by GeneralFormula (G1) include, but are not limited to, heterocyclic compoundsrepresented by Structural Formulae (100) to (174), (200) to (274), (300)to (374), (400) to (487), (500) to (574), and (600) to (674).

A variety of reactions can be applied to a method of synthesizing aheterocyclic compound of one embodiment of the present invention. Forexample, synthesis reactions described below enable the synthesis of aheterocyclic compound of one embodiment of the present inventionrepresented by General Formula (G1). Note that the method ofsynthesizing a heterocyclic compound which is one embodiment of thepresent invention is not limited to the synthesis methods below.

<Method 1 of Synthesizing Heterocyclic Compound Represented by GeneralFormula (G1)>

First, Synthesis Scheme (A-1) is illustrated below.

The heterocyclic compound (G1) of one embodiment of the presentinvention can be synthesized as illustrated in Synthesis Scheme (A-1).Specifically, a halide of a dibenzo[f,h]quinoxaline derivative(Compound 1) is coupled with boronic acid or an organoboron compound ofa carbazole derivative, a dibenzofuran derivative, or a dibenzothiophenederivative (Compound 2) by a Suzuki-Miyaura reaction, whereby theheterocyclic compound (G1) described in this embodiment can be obtained.

In Synthesis Scheme (A-1), A represents any of a substituted orunsubstituted carbazolyl group, a substituted or unsubstituteddibenzothiophenyl group, and a substituted or unsubstituteddibenzofuranyl group. Ar represents an arylene group having 6 to 13carbon atoms. The arylene group may have one or more substituents, andthe substituents may be bonded to form a ring. R¹¹ to R¹⁹ separatelyrepresent any of hydrogen, an alkyl group having 1 to 4 carbon atoms,and a substituted or unsubstituted aryl group having 6 to 13 carbonatoms. R⁵⁰ and R⁵¹ separately represent hydrogen or an alkyl grouphaving 1 to 6 carbon atoms. In Synthesis Scheme (A-1), R⁵⁰ and R⁵¹ maybe bonded to each other to form a ring. Further, X¹ represents ahalogen.

Examples of the palladium catalyst that can be used in Synthesis Scheme(A-1) include, but are not limited to, palladium(II) acetate,tetrakis(triphenylphosphine)palladium(0),bis(triphenylphosphine)palladium(II) dichloride, and the like.

Examples of the ligand of the palladium catalyst which can be used inSynthesis Scheme (A-1) include, but are not limited to,tri(ortho-tolyl)phosphine, triphenylphosphine, tricyclohexylphosphine,and the like.

Examples of the base that can be used in Synthesis Scheme (A-1) include,but are not limited to, organic bases such as sodium tert-butoxide,inorganic bases such as potassium carbonate and sodium carbonate, andthe like.

Examples of the solvent that can be used in Synthesis Scheme (A-1)include, but are not limited to, a mixed solvent of toluene and water; amixed solvent of toluene, alcohol such as ethanol, and water; a mixedsolvent of xylene and water; a mixed solvent of xylene, alcohol such asethanol, and water; a mixed solvent of benzene and water; a mixedsolvent of benzene, alcohol such as ethanol, and water; a mixed solventof water and an ether such as ethylene glycol dimethyl ether; and thelike. It is more preferable to use a mixed solvent of toluene and water,a mixed solvent of toluene, ethanol, and water, or a mixed solvent ofwater and an ether such as ethylene glycol dimethyl ether.

As a coupling reaction illustrated in Synthesis Scheme (A-1), theSuzuki-Miyaura reaction using the organoboron compound or the boronicacid represented by Compound 2 may be replaced with a cross couplingreaction using an organoaluminum compound, an organozirconium compound,an organozinc compound, an organotin compound, or the like. However, thepresent invention is not limited thereto.

Further, in the Suzuki-Miyaura Coupling Reaction illustrated inSynthesis Scheme (A-1), an organoboron compound or boronic acid of adibenzo[f,h]quinoxaline derivative may be coupled with a halide of acarbazole derivative, a dibenzofuran derivative, or a dibenzothiophenederivative or with a carbazole derivative, a dibenzofuran derivative, ora dibenzothiophene derivative which has a triflate group as asubstituent, by the Suzuki-Miyaura reaction.

Thus, a heterocyclic compound of this embodiment can be synthesized.

<Method 2 of Synthesizing Heterocyclic Compound Represented by GeneralFormula (G1)>

Another method of synthesizing the heterocyclic compound represented byGeneral Formula (G1) will be described below. First, Synthesis Scheme(B-1) in which a boron compound of A is used as a material isillustrated below.

As illustrated in Synthesis Scheme (B-1), a halide of adibenzo[f,h]quinoxaline derivative (Compound 3) is coupled with anorganoboron compound or boronic acid of a carbazole derivative, adibenzofuran derivative, or a dibenzothiophene derivative (Compound 4)by a Suzuki-Miyaura reaction, whereby the heterocyclic compound (G1)described in this embodiment can be obtained.

In Synthesis Scheme (B-1), A represents any of a substituted orunsubstituted carbazolyl group, a substituted or unsubstituteddibenzothiophenyl group, and a substituted or unsubstituteddibenzofuranyl group. Ar represents an arylene group having 6 to 13carbon atoms. The arylene group may have one or more substituents, andthe substituents may be bonded to form a ring. R¹¹ to R¹⁹ separatelyrepresent hydrogen, an alkyl group having 1 to 4 carbon atoms, or asubstituted or unsubstituted aryl group having 6 to 13 carbon atoms. R⁵²and R⁵³ separately represent hydrogen or an alkyl group having 1 to 6carbon atoms. In Synthesis Scheme (B-1), R⁵² and R⁵³ may be bonded toeach other to form a ring. Further, X² represents a halogen or atriflate group, and, as a halogen, preferably iodine or bromine.

Examples of the palladium catalyst that can be used in Synthesis Scheme(B-1) include, but are not limited to, palladium(II) acetate,tetrakis(triphenylphosphine)palladium(0),bis(triphenylphosphine)palladium(II) dichloride, and the like.

Examples of the ligand of the palladium catalyst which can be used inSynthesis Scheme (B-1) include, but are not limited to,tri(ortho-tolyl)phosphine, triphenylphosphine, tricyclohexylphosphine,and the like.

Examples of the base that can be used in Synthesis Scheme (B-1) include,but are not limited to, organic bases such as sodium tert-butoxide,inorganic bases such as potassium carbonate and sodium carbonate, andthe like.

Examples of the solvent that can be used in Synthesis Scheme (B-1)include, but are not limited to, a mixed solvent of toluene and water; amixed solvent of toluene, alcohol such as ethanol, and water; a mixedsolvent of xylene and water; a mixed solvent of xylene, alcohol such asethanol, and water; a mixed solvent of benzene and water; a mixedsolvent of benzene, alcohol such as ethanol, and water; a mixed solventof water and an ether such as ethylene glycol dimethyl ether; and thelike. It is more preferable to use a mixed solvent of toluene and water,a mixed solvent of toluene, ethanol, and water, or a mixed solvent ofwater and an ether such as ethylene glycol dimethyl ether.

As a coupling reaction illustrated in Synthesis Scheme (B-1), theSuzuki-Miyaura reaction using the organoboron compound or the boronicacid represented by Compound 4 may be replaced with a cross couplingreaction using an organoaluminum compound, an organozirconium compound,an organozinc compound, an organotin compound, or the like. However, thepresent invention is not limited thereto. Further, in this coupling, atriflate group or the like may be used other than a halogen; however,the present invention is not limited thereto.

Further, in the Suzuki-Miyaura Coupling Reaction illustrated inSynthesis Scheme (B-1), an organoboron compound or boronic acid of adibenzo[f,h]quinoxaline derivative may be coupled with a halide of acarbazole derivative, a dibenzofuran derivative, or a dibenzothiophenederivative or with a carbazole derivative, a dibenzofuran derivative, ora dibenzothiophene derivative which has a triflate group as asubstituent, by the Suzuki-Miyaura reaction.

To synthesize the heterocyclic compound represented by General Formula(G1) in which A is a substituted or unsubstituted N-carbazolyl group,the following Synthesis Scheme (B-2) is employed, thereby obtaining theheterocyclic compound represented by General Formula (G2-2).

As illustrated in Synthesis Scheme (B-2), a halide of adibenzo[f,h]quinoxaline derivative (Compound 3) is coupled with a9H-carbazole derivative (Compound 5) using a metal catalyst, metal, or ametal compound in the presence of a base, whereby the heterocycliccompound (G2-2) described in this embodiment can be obtained.

In Synthesis Scheme (B-2), R¹¹ to R¹⁹ separately represent hydrogen, analkyl group having 1 to 4 carbon atoms, or a substituted orunsubstituted aryl group having 6 to 13 carbon atoms. Ar represents anarylene group having 6 to 13 carbon atoms. The arylene group may haveone or more substituents, and the substituents may be bonded to form aring. R³¹ to R³⁸ separately represent hydrogen, an alkyl group having 1to 4 carbon atoms, or a substituted or unsubstituted aryl group having 6to 13 carbon atoms. Further, X³ represents a halogen or a triflategroup, and, as a halogen, preferably iodine or bromine.

In the case where the Hartwig-Buchwald reaction is performed inSynthesis Scheme (B-2), bis(dibenzylideneacetone)palladium(0),palladium(II) acetate, or the like can be given as the palladiumcatalyst that can be used.

Examples of the ligand of the palladium catalyst which can be used inSynthesis Scheme (B-2) include tri(tert-butyl)phosphine,tri(n-hexyl)phosphine, tricyclohexylphosphine, and the like.

Examples of the base that can be used in Synthesis Scheme (B-2) includeorganic bases such as sodium tert-butoxide, inorganic bases such aspotassium carbonate, and the like.

Examples of the solvent that can be used in Synthesis Scheme (B-2)include toluene, xylene, benzene, tetrahydrofuran, and the like.

Other than the Hartwig-Buchwald reaction, the Ullmann reaction or thelike may be used, and the reaction that can be used is not limited tothese.

Thus, the heterocyclic compound of this embodiment can be synthesized.

A heterocyclic compound of one embodiment of the present invention has awide band gap. Accordingly, by use of such a heterocyclic compound for alight-emitting element, as a host material of a light-emitting layer inwhich a light-emitting substance is dispersed, high current efficiencycan be obtained. In particular, a heterocyclic compound of oneembodiment of the present invention is suitably used as a host materialin which a phosphorescent compound is dispersed. Further, since aheterocyclic compound of this embodiment is a substance having a highelectron-transport property, it can be suitably used as a material foran electron-transport layer in a light-emitting element. By the use of aheterocyclic compound of this embodiment, a light-emitting elementhaving low driving voltage can be realized. In addition, alight-emitting element having high current efficiency can be realized. Alight-emitting element having a long lifetime can also be realized.Furthermore, by the use of this light-emitting element, a light-emittingdevice, an electronic device, and a lighting device each having reducedpower consumption can be obtained.

Embodiment 2

In Embodiment 2, light-emitting elements of embodiment of the presentinvention will be described with reference to FIGS. 1A and 1B.

One embodiment of the present invention is a light-emitting elementincluding a compound in which a dibenzo[f,h]quinoxaline ring and ahole-transport skeleton are bonded through an arylene group.

A compound with a quinoxaline skeleton has a high electron-transportproperty, and use of such a compound for a light-emitting elementenables the element to have low driving voltage. However, a quinoxalineskeleton has a planar structure. Since a compound having a planarstructure is easily crystallized when formed into a film, use of such acompound for light-emitting elements causes the elements to have a shorta lifetime. Furthermore, a quinoxaline skeleton is poor at acceptingholes. When a compound that cannot easily accept holes is used as a hostmaterial of a light-emitting layer, the region of electron-holerecombination concentrates on an interface of the light-emitting layer,leading to a reduction in the lifetime of the light-emitting element. Itis likely that these problems will be solved by the introduction of ahole-transport skeleton into the molecule. However, if a hole-transportskeleton is directly bonded to a quinoxaline skeleton, the conjugatedsystem extends to cause a decrease in band gap and a decrease in tripletexcitation energy.

Nevertheless, the present inventors have found that the above problemscan be solved by using, for a light-emitting element, a compound inwhich a dibenzo[P]quinoxaline ring and a hole-transport skeleton arebonded through an arylene group.

The above-described compound has a hole-transport skeleton in additionto a dibenzo[f,h]quinoxaline ring, making it easy to accept holes.Accordingly, by use of the compound as a host material of alight-emitting layer, electrons and holes recombine in thelight-emitting layer, so that it is possible to suppress the decrease inthe lifetime of the light-emitting element. Furthermore, theintroduction of a hole-transport skeleton enables the compound to have athree-dimensionally bulky structure, and the compound is difficult tocrystallize when formed into a film. By the use of the compound for alight-emitting element, the element can have a long lifetime. Moreover,in this compound, since a dibenzo[f,h]quinoxaline ring and ahole-transport skeleton are bonded through an arylene group, decreasesin band gap and triplet excitation energy can be prevented as comparedwith a compound in which a dibenzo[f,h]quinoxaline ring and ahole-transport skeleton are directly bonded. By the use of the compoundfor a light-emitting element, the element can have high currentefficiency.

Thus, the compound described above can be suitably used as a materialfor an organic device such as a light-emitting element or an organictransistor.

As the hole-transport skeleton, a π-electron rich heteroaromatic ring ispreferable. As the π-electron rich heteroaromatic ring, a carbazolering, a dibenzofuran ring, or a dibenzothiophene ring is preferable. Asthe arylene group, any of a substituted or unsubstituted phenylene groupand a substituted or unsubstituted biphenyldiyl group is preferable.

One embodiment of the present invention is a light-emitting elementincluding a heterocyclic compound represented by General Formula (G0)below.[Chemical Formula 75]E-Ar-A  (G0)

In General Formula (G0), A represents any of a substituted orunsubstituted carbazolyl group, a substituted or unsubstituteddibenzothiophenyl group, and a substituted or unsubstituteddibenzofuranyl group, E represents substituted or unsubstituteddibenzo[f,h]quinoxaline, and Ar represents an arylene group having 6 to13 carbon atoms. The arylene group may have one or more substituents,and the substituents may be bonded to form a ring.

Embodiment 2 gives descriptions of light-emitting elements eachincluding 2-[3-(dibenzothiophen-4-yl)phenyl]dibenzo[f,h]quinoxaline(abbreviation: 2mDBTPDBq-II) represented by Structural Formula (101) inEmbodiment 1, which is an example of the above compounds, referring toFIGS. 1A and 1B.

In a light-emitting element of this embodiment, the EL layer having atleast a light-emitting layer is interposed between a pair of electrodes.The EL layer may also have a plurality of layers in addition to thelight-emitting layer. The plurality of layers is a combination of alayer containing a substance having a high carrier-injection propertyand a layer containing a substance having a high carrier-transportproperty which are stacked so that a light-emitting region is formed ina region away from the electrodes, that is, so that carriers recombinein a region away from the electrodes. In this specification, the layercontaining a substance having a high carrier-injection or -transportproperty is also referred to as a functional layer which functions toinject or transport carriers, for example. As a functional layer, ahole-injection layer, a hole-transport layer, an electron-injectionlayer, an electron-transport layer, or the like can be used.

In the light-emitting element of this embodiment illustrated in FIG. 1A,an EL layer 102 having a light-emitting layer 113 is provided between apair of electrodes, a first electrode 101 and a second electrode 103.The EL layer 102 includes a hole-injection layer 111, a hole-transportlayer 112, the light-emitting layer 113, an electron-transport layer114, and an electron-injection layer 115. The light-emitting element inFIG. 1A includes the first electrode 101 formed over a substrate 100,the hole-injection layer 111, the hole-transport layer 112, thelight-emitting layer 113, the electron-transport layer 114, and theelectron-injection layer 115 which are stacked over the first electrode101 in this order, and the second electrode 103 provided thereover. Notethat, in the light-emitting element described in this embodiment, thefirst electrode 101 functions as an anode and the second electrode 103functions as a cathode.

The substrate 100 is used as a support of the light-emitting element.For example, glass, quartz, plastic, or the like can be used for thesubstrate 100. A flexible substrate may also be used. The flexiblesubstrate is a substrate that can be bent, such as a plastic substratemade of polycarbonate, polyarylate, or polyether sulfone, for example. Afilm (made of polypropylene, polyester, vinyl, polyvinyl fluoride, vinylchloride, or the like), an inorganic film formed by evaporation, or thelike can also be used. Note that materials other than these can be usedas long as they can function as a support of the light-emitting element.

For the first electrode 101, a metal, an alloy, an electricallyconductive compound, a mixture thereof, or the like which has a highwork function (specifically, a work function of 4.0 eV or more) ispreferably used. Specific examples include indium oxide-tin oxide (ITO:indium tin oxide), indium tin oxide containing silicon or silicon oxide,indium oxide-zinc oxide (IZO: indium zinc oxide), indium oxidecontaining tungsten oxide and zinc oxide (IWZO), and the like. Films ofthese conductive metal oxides are usually formed by sputtering; however,a sol-gel method or the like may also be used. For example, a film ofindium oxide-zinc oxide (IZO) can be formed by a sputtering method usinga target obtained by adding 1 wt % to 20 wt % of zinc oxide to indiumoxide. A film of indium oxide (IWZO) containing tungsten oxide and zincoxide can be formed by a sputtering method using a target obtained byadding 0.5 wt % to 5 wt % of tungsten oxide and 0.1 wt % to 1 wt % ofzinc oxide to indium oxide. Further, gold, platinum, nickel, tungsten,chromium, molybdenum, iron, cobalt, copper, palladium, nitrides of metalmaterials (e.g., titanium nitride), and the like can be given.

However, when a layer which is in contact with the first electrode 101and included in the EL layer 102 is formed using a composite materialincluding an organic compound and an electron acceptor (an acceptor)described later, the first electrode 101 can be formed using any of avariety of metals, alloys, and electrically conductive compounds, amixture thereof, and the like regardless of work function. For example,aluminum, silver, an alloy containing aluminum (e.g., Al—Si), or thelike can also be used.

The EL layer 102 formed over the first electrode 101 includes at leastthe light-emitting layer 113, and part of the EL layer 102 contains aheterocyclic compound which is one embodiment of the present invention.A known substance can also be used for part of the EL layer 102, andeither a low molecular compound or a high molecular compound can beused. Note that substances forming the EL layer 102 may consist oforganic compounds or may include an inorganic compound as a part.

As illustrated in FIGS. 1A and 1B, the EL layer 102 is formed bystacking as appropriate the hole-injection layer 111, the hole-transportlayer 112, the electron-transport layer 114, the electron-injectionlayer 115, and the like in combination as well as the light-emittinglayer 113.

The hole-injection layer 111 is a layer including a substance having ahigh hole-injection property. Examples of the substance having a highhole-injection property which can be used include metal oxides such asmolybdenum oxide, titanium oxide, vanadium oxide, rhenium oxide,ruthenium oxide, chromium oxide, zirconium oxide, hafnium oxide,tantalum oxide, silver oxide, tungsten oxide, and manganese oxide. Aphthalocyanine-based compound such as phthalocyanine (abbreviation:H₂Pc), or copper(II) phthalocyanine (abbreviation: CuPc) can also beused.

Any of the following aromatic amine compounds which are low molecularorganic compounds can also be used:4,4′,4″-tris(N,N-diphenylamino)triphenylamine (abbreviation: TDATA);4,4′,4″-tris[N-(3-methylphenyl)-N-phenylamino]triphenylamine(abbreviation: MTDATA);4,4′-bis[N-(4-diphenylaminophenyl)-N-phenylamino]biphenyl (abbreviation:DPAB);4,4′-bis(N-{4-[N′-(3-methylphenyl)-N′-phenylamino]phenyl}-N-phenylamino)biphenyl(abbreviation: DNTPD);1,3,5-tris[N-(4-diphenylaminophenyl)-N-phenylamino]benzene(abbreviation: DPA3B);3-[N-(9-phenylcarbazol-3-yl)-N-phenylamino]-9-phenylcarbazole(abbreviation: PCzPCA1);3,6-bis[N-(9-phenylcarbazol-3-yl)-N-phenylamino]-9-phenylcarbazole(abbreviation: PCzPCA2);3-[N-(1-naphthyl)-N-(9-phenylcarbazol-3-yl)amino]-9-phenylcarbazole(abbreviation: PCzPCN1); and the like.

High molecular compounds (such as oligomers, dendrimers, or polymers)can also be used. The following high molecular compounds can be given asexamples: poly(N-vinylcarbazole) (abbreviation: PVK);poly(4-vinyltriphenylamine) (abbreviation: PVTPA);poly[N-(4-{N′-[4-(4-diphenylamino)phenyl]phenyl-N′-phenylamino}phenyl)methacrylamide](abbreviation: PTPDMA);poly[N,N′-bis(4-butylphenyl)-N,N′-bis(phenyl)benzidine](abbreviation:Poly-TPD); and the like. A high molecular compound to which acid isadded, such as poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonicacid) (PEDOT/PSS), or polyaniline/poly(styrenesulfonic acid) (PAni/PSS),can also be used.

For the hole-injection layer 111, a composite material including anorganic compound and an electron acceptor (an acceptor) may be used.Such a composite material is excellent in a hole-injection property anda hole-transport property because the electron acceptor causesgeneration of holes. In this case, the organic compound is preferably amaterial excellent in transporting the generated holes (a substancehaving a high hole-transport property).

As the organic compound used for the composite material, a variety ofcompounds can be used, such as aromatic amine compounds, carbazolederivatives, aromatic hydrocarbons, and high molecular compounds (suchas oligomers, dendrimers, or polymers). The organic compound used forthe composite material is preferably an organic compound having a highhole-transport property. Specifically, a substance having a holemobility of 10⁻⁶ cm²/Vs or more is preferably used. Note that other thanthese substances, any substance that has a property of transporting moreholes than electrons may be used. The organic compounds which can beused for the composite material are specifically given below.

Examples of the organic compounds that can be used for the compositematerial include: aromatic amine compounds such as TDATA, MTDATA, DPAB,DNTPD, DPA3B, PCzPCA1, PCzPCA2, PCzPCN1,4,4′-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (abbreviation: NPB orα-NPD), andN,N′-bis(3-methylphenyl)-N,N′-diphenyl-[1,1′-biphenyl]-4,4′-diamine(abbreviation: TPD) 4-phenyl-4′-(9-phenylfluoren-9-yl)triphenylamine(abbreviation: BPAFLP); and carbazole derivatives such as4,4′-di(N-carbazolyl)biphenyl (abbreviation: CBP),1,3,5-tris[4-(N-carbazolyl)phenyl]benzene (abbreviation: TCPB),9-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazole (abbreviation: CzPA),9-phenyl-3-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazole (abbreviation:PCzPA), and 1,4-bis[4-(N-carbazolyl)phenyl-2,3,5,6-tetraphenylbenzene.

Any of the following aromatic hydrocarbon compounds can be used:2-tert-butyl-9,10-di(2-naphthyl)anthracene (abbreviation: t-BuDNA);2-tert-butyl-9,10-di(1-naphthyl)anthracene,9,10-bis(3,5-diphenylphenyl)anthracene (abbreviation: DPPA);2-tert-butyl-9,10-bis(4-phenylphenyl)anthracene (abbreviation: t-BuDBA);9,10-di(2-naphthyl)anthracene (abbreviation: DNA);9,10-diphenylanthracene (abbreviation: DPAnth); 2-tert-butylanthracene(abbreviation: t-BuAnth); 9,10-bis(4-methyl-1-naphthyl)anthracene(abbreviation: DMNA);9,10-bis[2-(1-naphthyl)phenyl)-2-tert-butylanthracene;9,10-bis[2-(1-naphthyl)phenyl]anthracene; and2,3,6,7-tetramethyl-9,10-di(1-naphthyl)anthracene.

Any of the following aromatic hydrocarbon compounds can be used:2,3,6,7-tetramethyl-9,10-di(2-naphthyl)anthracene; 9,9′-bianthryl;10,10′-diphenyl-9,9′-bianthryl;10,10′-bis(2-phenylphenyl)-9,9′-bianthryl;10,10′-bis[(2,3,4,5,6-pentaphenyl)phenyl]-9,9′-bianthryl; anthracene;tetracene; rubrene; perylene; 2,5,8,11-tetra(tert-butyl)perylene;pentacene; coronene, 4,4′-bis(2,2-diphenylvinyl)biphenyl (abbreviation:DPVBi); and 9,10-bis[4-(2,2-diphenylvinyl)phenyl]anthracene(abbreviation: DPVPA).

As the electron acceptor, organic compounds such as7,7,8,8-tetracyano-2,3,5,6-tetrafluoroquinodimethane (abbreviation:F₄-TCNQ) and chloranil and transition metal oxides can be given. Oxidesof metals belonging to Groups 4 to 8 in the periodic table can be alsogiven. Specifically, vanadium oxide, niobium oxide, tantalum oxide,chromium oxide, molybdenum oxide, tungsten oxide, manganese oxide, andrhenium oxide are preferable since their electron-accepting property ishigh. Among these, molybdenum oxide, which is easy to handle owing toits stability in the air and low hygroscopic property, is especiallypreferable.

Note that the composite material may be formed using a high molecularcompound such as PVK, PVTPA, PTPDMA, or Poly-TPD and an electronacceptor, which are described above, so as to be used for thehole-injection layer 111.

The hole-transport layer 112 is a layer including a substance having ahigh hole-transport property. As the substance having a highhole-transport property, any of the following aromatic amine compoundscan be used, for example: NPB; TPD; BPAFLP;4,4′-bis[N-(9,9-dimethylfluoren-2-yl)-N-phenylamino]biphenyl(abbreviation: DFLDPBi); and4,4′-bis[N-(spiro-9,9′-bifluoren-2-yl)-N-phenylamino]biphenyl(abbreviation: BSPB). The substances given here are mainly substanceshaving a hole mobility of 10⁻⁶ cm²/Vs or more. Note that other thanthese substances, any substance that has a property of transporting moreholes than electrons may be used. The layer including a substance havinga high hole-transport property is not limited to a single layer, and maybe a stack of two or more layers containing any of the above substances.

For the hole-transport layer 112, a carbazole derivative such as CBP,CzPA, or PCzPA or an anthracene derivative such as t-BuDNA, DNA, orDPAnth may also be used.

For the hole-transport layer 112, a high molecular compound such as PVK,PVTPA, PTPDMA, or Poly-TPD can also be used.

The light-emitting layer 113 is a layer including a light-emittingsubstance. Note that in Embodiment 2, the case where 2mDBTPDBq-IIdescribed in Embodiment 1 is used for the light-emitting layer isdescribed. For the light-emitting layer in which a light-emittingsubstance (a guest material) is dispersed in another substance (a hostmaterial), 2mDBTPDBq-II can be used as the host material. The guestmaterial which is a light-emitting substance is dispersed in2mDBTPDBq-II, whereby light emission can be obtained from the guestmaterial. Thus, a compound of one embodiment of the present invention,in which a dibenzo[f,h]quinoxaline ring and a hole-transport skeletonare bonded through an arylene group, is effective in its use as a hostmaterial in a light-emitting layer.

In addition, more than one kind of substances can be used as thesubstances (host materials) in which the light-emitting substance (guestmaterial) is dispersed. The light-emitting layer may thus includeanother material as a host material in addition to 2mDBTPDBq-II.

As the light-emitting substance, for example, a fluorescent compoundwhich emits fluorescence or a phosphorescent compound which emitsphosphorescence can be used. The phosphorescent compounds that can beused for the light-emitting layer 113 will be given. Examples of thematerials that emits blue light includeN,N′-bis[4-(9H-carbazol-9-yl)phenyl]-N,N′-diphenylstilbene-4,4′-diamine(abbreviation: YGA2S),4-(9H-carbazol-9-yl)-4′-(10-phenyl-9-anthryl)triphenylamine(abbreviation: YGAPA),4-(10-phenyl-9-anthryl)-4′-(9-phenyl-9H-carbazol-3-yl)triphenylamine(abbreviation: PCBAPA), and the like. In addition, examples of thematerials that emits green light includeN-(9,10-diphenyl-2-anthryl)-N,9-diphenyl-9H-carbazol-3-amine(abbreviation: 2PCAPA),N-[9,10-bis(1,1′-biphenyl-2-yl)-2-anthryl]-N,9-diphenyl-9H-carbazol-3-amine(abbreviation: 2PCABPhA),N-(9,10-diphenyl-2-anthryl)-N,N′,N′-triphenyl-1,4-phenylenediamine(abbreviation: 2DPAPA),N-[9,10-bis(1,1′-biphenyl-2-yl)-2-anthryl]-N,N′,N′-triphenyl-1,4-phenylenediamine(abbreviation: 2DPABPhA),N-[9,10-bis(1,1′-biphenyl-2-yl)]-N-[4-(9H-carbazol-9-yl)phenyl]-N-phenylanthracen-2-amine(abbreviation: 2YGABPhA), N,N,9-triphenylanthracen-9-amine(abbreviation: DPhAPhA), and the like. Further, examples of thematerials that emits yellow light include rubrene,5,12-bis(1,1′-biphenyl-4-yl)-6,11-diphenyltetracene (abbreviation: BPT),and the like. Furthermore, examples of the materials that emits redlight include N,N,N′,N′-tetrakis(4-methylphenyl)tetracene-5,11-diamine(abbreviation: p-mPhTD),7,14-diphenyl-N,N,N′,N′-tetrakis(4-methylphenyeacenaphtho[1,2-a]fluoranthene-3,10-diamine(abbreviation: p-mPhAFD), and the like.

In addition, the phosphorescent compounds that can be used for thelight-emitting layer 113 will be given. Examples of the materials thatemits green light include tris(2-phenylpyridinato-N,C^(2′))iridium(III)(abbreviation: [Ir(ppy)₃]),bis(2-phenylpyridinato-N,C^(2′))iridium(III)acetylacetonate(abbreviation: [Ir(ppy)₂(acac)]),bis(1,2-diphenyl-1H-benzimidazolato)iridium(III)acetylacetonate(abbreviation: [Ir(pbi)₂(acac)]),bis(benzo[h]quinolinato)iridium(III)acetylacetonate (abbreviation:[Ir(bzq)₂(acac)]), tris(benzo[h]quinolinato)iridium(III) (abbreviation:[Ir(bzq)₃]), and the like. Examples of the materials that emits yellowlight includebis(2,4-diphenyl-1,3-oxazolato-N,C^(2′))iridium(III)acetylacetonate(abbreviation: [Ir(dpo)₂(acac)]),bis[2-(4′-(perfluorophenylphenyl)pyridinato]iridium(III)acetylacetonate(abbreviation: [Ir(p-PF-ph)₂(acac)]),bis(2-phenylbenzothiazolato-N,C^(2′))iridium(III)acetylacetonate(abbreviation: [Ir(bt)₂(acac)]),(acetylacetonato)bis[2,3-bis(4-fluorophenyl)-5-methylpyrazinato]iridium(III)(abbreviation: [Ir(Fdppr-Me)₂(acac)]),(acetylacetonato)bis[2-(4-methoxyphenyl)-3,5-dimethylpyrazinato]iridium(III)(abbreviation: [Ir(dmmoppr)₂(acac)]), and the like. Examples of thematerials that emits orange light includetris(2-phenylquinolinato-N,C^(2′))iridium(III) (abbreviation:[Ir(pq)₃]), bis(2-phenylquinolinato-N,C^(2′))iridium(III)acetylacetonate(abbreviation: [Ir(pq)₂(acac)]),(acetylacetonato)bis(3,5-dimethyl-2-phenylpyrazinato)iridium(III)(abbreviation: [Ir(mppr-Me)₂(acac)]),(acetylacetonato)bis(5-isopropyl-3-methyl-2-phenylpyrazinato)iridium(III)(abbreviation: [Ir(mppr-iPr)₂(acac)]), and the like. Examples of thematerials that emits red light include organometallic complexes such asbis[2-(2′-benzo[4,5-α]thienyl)pyridinato-N,C^(3′))iridium(III)acetylacetonate (abbreviation: [Ir(btp)₂(acac)]),bis(1-phenylisoquinolinato-N,C^(2′))iridium(III)acetylacetonate(abbreviation: [Ir(piq)₂(acac]),(acetylacetonato)bis[2,3-bis(4-fluorophenyl)quinoxalinato]iridium(III)(abbreviation: [Ir(Fdpq)₂(acac)]),acetylacetonato)bis(2,3,5-triphenylpyrazinato)iridium(III)(abbreviation: [Ir(tppr)₂(acac)]),(dipivaloylmethanato)bis(2,3,5-triphenylpyrazinato)iridium(III)(abbreviation: [Ir(tppr)₂(dpm)]), and(2,3,7,8,12,13,17,18-octaethyl-21H,23H-porphine)platinum(II)(abbreviation: PtOEP). Any of the following rare-earth metal complexescan be used as a phosphorescent compound:tris(acetylacetonato)(monophenanthroline)terbium(III) (abbreviation:[Tb(acac)₃(Phen)]);tris(1,3-diphenyl-1,3-propanedionato)(monophenanthroline)europium(III)(abbreviation: [Eu(DBM)₃(Phen)]); andtris[1-(2-thenoyl)-3,3,3-trifluoroacetonato](monophenanthroline)europium(III)(abbreviation: [Eu(TTA)₃(Phen)]), because light emission is from arare-earth metal ion (electron transfer between differentmultiplicities) in such a rare-earth metal complex.

Note that in a compound which is one embodiment of the presentinvention, in which a dibenzo[f,h]quinoxaline ring and a hole-transportskeleton are bonded through an arylene group, a dibenzo[f,h]quinoxalineskeleton is considered as the skeleton where the LUMO level ispredominantly located. Further, the compound has a deep LUMO level of atleast −2.8 eV or less, specifically −2.9 eV or less on the basis ofcyclic voltammetry (CV) measurements. For example, the LUMO level of2mDBTPDBq-II is found to be −2.96 eV by CV measurements. Furthermore,the LUMO level of the above-described phosphorescent compound having apyrazine skeleton, such as [Ir(mppr-Me)₂(acac)], [Ir(mppr-iPr)₂(acac)],[Ir(tppr)₂(acac)], or [Ir(tppr)₂(dpm)], is substantially equally deep.Therefore, when a light-emitting layer includes a compound of oneembodiment of the present invention, in which a dibenzo[f,h]quinoxalinering and a hole-transport skeleton are bonded through an arylene group,as a host material, and a phosphorescent compound having a pyrazineskeleton as a guest material, traps for electrons in the light-emittinglayer can be reduced to a minimum, and extremely low-voltage driving canbe realized.

As the light-emitting substance, a high molecular compound can be used.Specifically, examples of the materials that emits blue light includepoly(9,9-dioctylfluorene-2,7-diyl) (abbreviation: PFO),poly[(9,9-dioctylfluorene-2,7-diyl)-co-(2,5-dimethoxybenzene-1,4-diyl)](abbreviation: PF-DMOP),poly{(9,9-dioctylfluorene-2,7-diyl)-co-[N,N′-di-(p-butylphenyl)-1,4-diaminobenzene]}(abbreviation: TAB-PFH), and the like. Further, examples of thematerials that emits green light include poly(p-phenylenevinylene)(abbreviation: PPV),poly[(9,9-dihexylfluorene-2,7-diyl)-alt-co-(benzo[2,1,3]thiadiazole-4,7-diyl)](abbreviation: PFBT),poly[(9,9-dioctyl-2,7-divinylenefluorenylene)-alt-co-(2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylene)],and the like. Furthermore, examples of the materials that emits orangeto red light includepoly[2-methoxy-5-(2′-ethylhexoxy)-1,4-phenylenevinylene] (abbreviation:MEH-PPV), poly(3-butylthiophene-2,5-diyl) (abbreviation: R4-PAT),poly{[9,9-dihexyl-2,7-bis(1-cyanovinylene)fluorenylene]-alt-co-[2,5-bis(N,N′-diphenylamino)-1,4-phenylene]},poly{[2-methoxy-5-(2-ethylhexyloxy)-1,4-bis(1-cyanovinylenephenylene)]-alt-co-[2,5-bis(N,N′-diphenylamino)-1,4-phenylene]}(abbreviation: CN-PPV-DPD), and the like.

The electron-transport layer 114 is a layer including a substance havinga high electron-transport property. As the substance having a highelectron-transport property, the following metal complexes having aquinoline skeleton or a benzoquinoline skeleton can be given:tris(8-quinolinolato)aluminum (abbreviation: Alq);tris(4-methyl-8-quinolinolato)aluminum (abbreviation: Almq₃);bis(10-hydroxybenzo[h]-quinolinato)beryllium (abbreviation: BeBq₂); andbis(2-methyl-8-quinolinolato)(4-phenylphenolato)aluminum (abbreviation:BAlq). A metal complex having an oxazole-based or thiazole-based ligand,such as bis[2-(2-hydroxyphenyl)benzoxazolato]zinc (abbreviation:Zn(BOX)₂) or bis[2-(2-hydroxyphenyl)benzothiazolato]zinc (abbreviation:Zn(BTZ)₂), or the like can also be used. Other than metal complexes,2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (abbreviation:PBD), 1,3-bis[5-(p-tert-butylphenyl)-1,3,4-oxadiazol-2-yl]benzene(abbreviation: OXD-7),3-(4-biphenylyl)-4-phenyl-5-(4-tert-butylphenyl)-1,2,4-triazole(abbreviation: TAZ), bathophenanthroline (abbreviation: BPhen),bathocuproine (abbreviation: BCP), or the like can be used. Thesubstances described here are mainly materials having an electronmobility of 10⁻⁶ cm²/Vs or more. Further, the electron-transport layeris not limited to a single layer, and may be a stack of two or morelayers containing any of the above substances are stacked.

The electron-injection layer 115 is a layer including a substance havinga high electron-injection property. For the electron-injection layer115, an alkali metal, an alkaline-earth metal, or a compound thereof,such as lithium, cesium, calcium, lithium fluoride, cesium fluoride,calcium fluoride, or lithium oxide, can be used. A rare-earth metalcompound like erbium fluoride can also be used. The above-mentionedsubstances for forming the electron-transport layer 114 can also beused.

Alternatively, a composite material including an organic compound and anelectron donor (a donor) may be used for the electron-injection layer115. Such a composite material is excellent in an electron-injectionproperty and an electron-transport property because the electron donorcauses generation of electrons. In this case, the organic compound ispreferably a material excellent in transporting the generated electrons.Specifically, for example, the substances for forming theelectron-transport layer 114 (e.g., a metal complex or a heteroaromaticcompound), which are described above, can be used. The electron donor ispreferably a substance showing an electron-donating property withrespect to the organic compound. Specifically, an alkali metal, analkaline-earth metal, and a rare-earth metal are preferable, andlithium, cesium, magnesium, calcium, erbium, ytterbium, and the like canbe given. Alkali metal oxides or alkaline-earth metal oxides are alsopreferable and lithium oxide, calcium oxide, barium oxide, and the likecan be given. A Lewis base such as magnesium oxide can also be used. Anorganic compound such as tetrathiafulvalene (abbreviation: TTF) can alsobe used.

The hole-injection layer 111, the hole-transport layer 112, thelight-emitting layer 113, the electron-transport layer 114, and theelectron-injection layer 115, which are described above, can each beformed by a method such as an evaporation method (including a vacuumevaporation method), an inkjet method, or a coating method.

When the second electrode 103 functions as a cathode, the secondelectrode 103 is preferably formed using a metal, an alloy, anelectrically-conductive compound, a mixture thereof, or the like havinga low work function (preferably, a work function of 3.8 eV or less).Specifically, any of the following can be used: elements belonging toGroup 1 or Group 2 of the periodic table, that is, alkali metals such aslithium and cesium, alkaline-earth metals such as magnesium, calcium,and strontium, or alloys thereof (e.g., Mg—Ag or Al—Li]); rare-earthmetals such as europium or ytterbium or alloys thereof; aluminum;silver; and the like.

However, when a layer which is in contact with the second electrode 103and included in the EL layer 102 is formed using a composite materialincluding an organic compound and an electron donor (a donor) describedabove, a variety of conductive materials such as aluminum, silver, ITO,and indium tin oxide containing silicon or silicon oxide can be usedregardless of work function.

Note that the second electrode 103 can be formed by a vacuum evaporationmethod or a sputtering method. In the case where a silver paste or thelike is used, a coating method, an inkjet method, or the like can beused.

In the above-described light-emitting element, a current flows due to apotential difference generated between the first electrode 101 and thesecond electrode 103, and holes and electrons recombine in the EL layer102, so that light is emitted. Then, this emitted light is extracted outthrough one or both of the first electrode 101 and the second electrode103. One or both of the first electrode 101 and the second electrode 103are thus have a property of transmitting visible light.

Further, the structure of the layers provided between the firstelectrode 101 and the second electrode 103 is not limited to the abovedescribed structure. A structure other than the above may alternativelybe employed as long as a light-emitting region in which holes andelectrons recombine is provided in a portion away from the firstelectrode 101 and the second electrode 103 in order to prevent quenchingdue to proximity of the light-emitting region to metal.

In other words, there is no particular limitation on a stack structureof the layers. A layer including a substance having a highelectron-transport property, a substance having a high hole-transportproperty, a substance having a high electron-injection property, asubstance having a high hole-injection property, a bipolar substance (asubstance having a high electron-transport property and a highhole-transport property), a hole-blocking material, or the like mayfreely be combined with a light-emitting layer including 2mDBTPDBq-II asa host material.

Since 2mDBTPDBq-II is a substance having a high electron-transportproperty, 2mDBTPDBq-II can also be used for the electron-transportlayer. In other words, a compound of one embodiment of the presentinvention, in which a dibenzo[f,h]quinoxaline ring and a hole-transportskeleton are bonded through an arylene group, can be used for theelectron-transport layer.

Furthermore, if a compound of one embodiment of the present invention,in which a dibenzo[f,h]quinoxaline ring and a hole-transport skeletonare bonded through an arylene group, is applied to both thelight-emitting layer (especially as a host material in thelight-emitting layer) and the electron-transport layer, extremelylow-voltage driving can be realized.

In the light-emitting element illustrated in FIG. 1B, the EL layer 102is provided between the first electrode 101 and the second electrode 103over the substrate 100. The EL layer 102 includes the hole-injectionlayer 111, the hole-transport layer 112, the light-emitting layer 113,the electron-transport layer 114, and the electron-injection layer 115.The light-emitting element in FIG. 1B includes the second electrode 103serving as a cathode over the substrate 100, the electron-injectionlayer 115, the electron-transport layer 114, the light-emitting layer113, the hole-transport layer 112, and the hole-injection layer 111which are stacked over the second electrode 103 in this order, and thefirst electrode 101 provided thereover which serves as an anode.

A method of forming the light-emitting element will now be specificallydescribed.

In a light-emitting element of this embodiment, the EL layer isinterposed between the pair of electrodes. The EL layer has at least thelight-emitting layer, and the light-emitting layer is formed using2mDBTPDBq-II as a host material. Further, the EL layer may include afunctional layer (e.g., the hole-injection layer, the hole-transportlayer, the electron-transport layer, or the electron-injection layer) inaddition to the light-emitting layer. The electrodes (the firstelectrode and the second electrode), the light-emitting layer, and thefunctional layer may be formed by any of the wet processes such as adroplet discharging method (an inkjet method), a spin coating method,and a printing method, or by a dry processes such as a vacuumevaporation method, a CVD method, and a sputtering method. A wet processallows formation at atmospheric pressure with a simple device and by asimple process, thereby having the effects of simplifying the processand improving productivity. In contrast, a dry process does not needdissolution of a material and enables use of a material that has lowsolubility in a solution, thereby expanding the range of materialchoices.

All the thin films included in a light-emitting element may be formed bya wet method. In this case, the light-emitting element can bemanufactured with only facilities needed for a wet process.Alternatively, the following method may be employed: formation of thestacked layers up to formation of the light-emitting layer is performedby a wet process whereas the functional layer, the first electrode, andthe like which are stacked over the light-emitting layer are formed by adry process. Further alternatively, the following method may beemployed: the second electrode and the functional layer are formed by adry process before the formation of the light-emitting layer whereas thelight-emitting layer, the functional layer stacked thereover, and thefirst electrode are formed by a wet process. Needless to say, thisembodiment is not limited to these, and a light-emitting element can beformed by appropriate selection from a wet method and a dry methoddepending on a material to be used, necessary film thickness, and theinterface state.

In this embodiment, a light-emitting element is fabricated over asubstrate made of glass, plastic or the like. By forming a plurality ofsuch light-emitting elements over one substrate, a passive matrixlight-emitting device can be manufactured. Further, a light-emittingelement may be fabricated in such a manner that a thin film transistor(TFT), for example, is be formed over a substrate made of glass,plastic, or the like and the element is formed over an electrodeelectrically connected to the TFT. Thus, an active matrix light-emittingdevice in which the TFT controls the driving of the light-emittingelement can be manufactured. Note that there is no particular limitationon the structure of the TFT. Either a staggered TFT or an invertedstaggered TFT may be employed. In addition, there is no particularlimitation on the crystallinity of a semiconductor used for the TFT, andan amorphous semiconductor or a crystalline semiconductor may be used.In addition, a driver circuit formed over a TFT substrate may be formedwith both n-channel TFTs and p-channel TFTs or may be formed with eithern-channel TFTs or p-channel TFTs.

Thus, a light-emitting element can be fabricated using 2mDBTPDBq-IIdescribed in Embodiment 1. By the use of a compound of one embodiment ofthe present invention, in which a dibenzo[f,h]quinoxaline ring and ahole-transport skeleton are bonded through an arylene group, for alight-emitting element, the light-emitting element can have low drivingvoltage, high current efficiency, and a long lifetime.

Furthermore, a light-emitting device (such as an image display device)using a light-emitting element of one embodiment of the presentinvention which is obtained as above can have low power consumption.

Note that, by the use of a light-emitting element described in thisembodiment, it is possible to fabricate a passive matrix light-emittingdevice or an active matrix light-emitting device in which a thin filmtransistor (TFT) controls the driving of the light-emitting element.

This embodiment can be implemented in appropriate combination with anyof the other embodiments.

Embodiment 3

In this embodiment, modes of light-emitting elements having a structurein which a plurality of light-emitting units is stacked (hereinafter,referred to as a stacked-type element) will be described with referenceto FIGS. 2A and 2B. These light-emitting element are each alight-emitting element including a plurality of light-emitting unitsbetween a first electrode and a second electrode.

In FIG. 2A, a first light-emitting unit 311 and a second light-emittingunit 312 are stacked between a first electrode 301 and a secondelectrode 303. In this embodiment, the first electrode 301 functions asan anode and the second electrode 303 functions as a cathode. The firstelectrode 301 and the second electrode 303 can be the same as those inEmbodiment 2. Further, the first light-emitting unit 311 and the secondlight-emitting unit 312 may have the same or different structures. Thefirst light-emitting unit 311 and the second light-emitting unit 312 maybe the same as those in Embodiment 2, or either of the units may be thesame as that in Embodiment 2.

Further, a charge generation layer 313 is provided between the firstlight-emitting unit 311 and the second light-emitting unit 312. When avoltage is applied between the first electrode 301 and the secondelectrode 303, the charge generation layer 313 functions to injectelectrons into one light-emitting unit and inject holes into the otherlight-emitting unit. In this embodiment, when a voltage is applied tothe first electrode 301 so that the potential thereof is higher thanthat of the second electrode 303, the charge generation layer 313injects electrons into the first light-emitting unit 311 and injectsholes into the second light-emitting unit 312.

Note that the charge generation layer 313 preferably has a property oftransmitting visible light in terms of light extraction efficiency.Further, the charge generation layer 313 functions even when it haslower conductivity than the first electrode 301 or the second electrode303.

The charge generation layer 313 may have either a structure including anorganic compound having a high hole-transport property and an electronacceptor (an acceptor) or a structure including an organic compoundhaving a high electron-transport property and an electron donor (adonor). Alternatively, both of these structures may be stacked.

In the case of the structure in which an electron acceptor is added toan organic compound having a high hole-transport property, any of thefollowing substances can be used as the organic compound having a highhole-transport property, for example: the heterocyclic compounds ofembodiments of the present invention; aromatic amine compounds such asNPB, TPD, TDATA, MTDATA, and4,4′-bis[N-(spiro-9,9′-bifluoren-2-yl)-N-phenylamino]biphenyl(abbreviation: BSPB); or the like. The substances given here are mainlymaterials having a hole mobility of 10⁻⁶ cm²/Vs or more. Note that otherthan the above substances, any organic compound that has a property oftransporting more holes than electrons may be used.

Further, as the electron acceptor,7,7,8,8-tetracyano-2,3,5,6-tetrafluoroquinodimethane (abbreviation:F₄-TCNQ), chloranil, and the like can be given. In addition, transitionmetal oxides can be given. Moreover, oxides of metals belonging toGroups 4 to 8 of the periodic table can be given. Specifically, vanadiumoxide, niobium oxide, tantalum oxide, chromium oxide, molybdenum oxide,tungsten oxide, manganese oxide, and rhenium oxide are preferablebecause they have a high electron-accepting property. Among these metaloxides, molybdenum oxide, which is easy to handle, is preferred owing toits stability in air and low hygroscopic property.

In contrast, in the case of the structure in which an electron donor isadded to an organic compound having a high electron-transport property,as the organic compound having a high electron-transport property, ametal complex having a quinoline skeleton or a benzoquinoline skeleton,such as Alq, Almq₃, BeBq₂, or BAlq, or the like can be used, forexample. A metal complex having an oxazole-based ligand or athiazole-based ligand, such as Zn(BOX)₂ or Zn(BTZ)₂ can also be used.Other than such metal complexes, PBD, OXD-7, TAZ, BPhen, BCP, or thelike can be used. The substances given here are mainly materials havingan electron mobility of 10⁻⁶ cm²/Vs or more. Note that other than theabove substances, any organic compound that has a property oftransporting more electrons than holes may be used.

Further, as the electron donor, any of alkali metals, alkaline-earthmetals, rare-earth metals, metals belonging to Group 13 of the periodictable, or oxides or carbonates thereof can be used. Specifically,lithium, cesium, magnesium, calcium, ytterbium, indium, lithium oxide,cesium carbonate, or the like is preferably used. An organic compoundsuch as tetrathianaphthacene may also be used as the electron donor.

Note that by the formation of the charge generation layer 313 using amaterial described above, it is possible to suppress an increase indriving voltage caused by stacking the EL layers.

In this embodiment, the light-emitting element having two light-emittingunits is described, and a light-emitting element having a stack of threeor more light-emitting units can also be employed as illustrated in FIG.2B. A plurality of light-emitting units which are partitioned by acharge generation layer is arranged between a pair of electrodes, as inthe light-emitting element according to this embodiment, whereby it ispossible to realize an element having a long lifetime which can emitlight with a high luminance while current density is kept low.

With light-emitting units having emission colors different from eachother, the light-emitting element as a whole can be made to emit lightwith a desired color. For example, in a light-emitting element havingtwo light-emitting units, the emission colors of the firstlight-emitting unit and the second light-emitting unit are madecomplementary; thus, the light-emitting element which emits white lightas a whole can be obtained. Note that the term “complementary” meanscolor relationship in which an achromatic color is obtained when colorsare mixed. That is, white light emission can be obtained by mixture oflight obtained from substances emitting lights with complementarycolors. The same can be applied to a light-emitting element which hasthree light-emitting units. For example, the light-emitting element as awhole can emit white light when the emission color of the firstlight-emitting unit is red, the emission color of the secondlight-emitting unit is green, and the emission color of the thirdlight-emitting unit is blue.

Note that this embodiment can be combined with any other embodiment asappropriate.

Embodiment 4

In Embodiment 4, a light-emitting device having a light-emitting elementof one embodiment of the present invention will be described withreference to FIGS. 3A and 3B. Note that FIG. 3A is a top viewillustrating the light-emitting device, and FIG. 3B is a cross-sectionalview taken along lines A-B and C-D of FIG. 3A.

In FIG. 3A, reference numeral 401 denotes a driver circuit portion (asource driver circuit), reference numeral 402 denotes a pixel portion,and reference numeral 403 denotes a driver circuit portion (a gatedriver circuit), which are each indicated by dotted lines. Referencenumeral 404 denotes a sealing substrate, reference numeral 405 denotes asealant, and a portion enclosed by the sealant 405 is a space.

Note that a lead wiring 408 is a wiring for transmitting signals thatare to be inputted to the source driver circuit 401 and the gate drivercircuit 403, and receives a video signal, a clock signal, a startsignal, a reset signal, and the like from an FPC (flexible printedcircuit) 409 which serves as an external input terminal. Although onlythe FPC is illustrated here, a printed wiring board (PWB) may beattached to the FPC. The light-emitting device in this specificationincludes not only a light-emitting device itself but also alight-emitting device to which an FPC or a PWB is attached.

Next, a cross-sectional structure will be described with reference toFIG. 3B. The driver circuit portion and the pixel portion are formedover an element substrate 410. Here, the source driver circuit 401 whichis the driver circuit portion and one pixel in the pixel portion 402 areillustrated.

Note that as the source driver circuit 401, a CMOS circuit whichincludes an n-channel TFT 423 and a p-channel TFT 424 is formed. Thedriver circuit may be any of a variety of circuits formed with TFTs,such as a CMOS circuit, a PMOS circuit, or an NMOS circuit. Although adriver-integrated type in which a driver circuit is formed over thesubstrate is described in this embodiment, the present invention is notlimited to this type, and the driver circuit can be formed outside thesubstrate.

The pixel portion 402 includes a plurality of pixels having a switchingTFT 411, a current control TFT 412, and a first electrode 413electrically connected to a drain of the current control TFT 412. Notethat an insulator 414 is formed to cover an end portion of the firstelectrode 413. Here, the insulator 414 is formed by using a positivetype photosensitive acrylic resin film.

In order to improve coverage, the insulator 414 is provided such thateither an upper end portion or a lower end portion of the insulator 414has a curved surface with a curvature. For example, when positivephotosensitive acrylic is used as a material for the insulator 414, itis preferable that only an upper end portion of the insulator 414 have acurved surface with a radius of curvature (0.2 μm to 3 μm). For theinsulator 414, it is also possible to use either a negative type thatbecomes insoluble in an etchant by light irradiation or a positive typethat becomes soluble in an etchant by light irradiation.

A light-emitting layer 416 and a second electrode 417 are formed overthe first electrode 413. Here, as a material for forming the firstelectrode 413 functioning as the anode, a material having a high workfunction is preferably used. For example, it is possible to use a singlelayer of an ITO film, an indium tin oxide film that includes silicon, anindium oxide film that includes 2 wt % to 20 wt % of zinc oxide, atitanium nitride film, a chromium film, a tungsten film, a Zn film, a Ptfilm, or the like, a stacked layer of a titanium nitride film and a filmthat mainly includes aluminum, a three-layer structure of a titaniumnitride film, a film that mainly includes aluminum and a titaniumnitride film, or the like. Note that, when a stacked layer structure isemployed, resistance of a wiring is low and a favorable ohmic contact isobtained.

In addition, the light-emitting layer 416 is formed by any of variousmethods such as an evaporation method using an evaporation mask, adroplet discharging method like an inkjet method, a printing method, anda spin coating method. The light-emitting layer 416 includes aheterocyclic compound described in Embodiment 1. Further, anothermaterial included in the light-emitting layer 416 may be a low molecularmaterial, an oligomer, a dendrimer, a high molecular material, or thelike.

As a material used for the second electrode 417 which is formed over thelight-emitting layer 416 and serves as a cathode, it is preferable touse a material having a low work function (e.g., Al, Mg, Li, Ca, or analloy or a compound thereof such as Mg—Ag, Mg—In, Al—Li, LiF, or CaF₂).In order that light generated in the light-emitting layer 416 betransmitted through the second electrode 417, a stack of a metal thinfilm having a reduced thickness and a transparent conductive film (e.g.,ITO, indium oxide containing 2 wt % to 20 wt % of zinc oxide, indiumoxide-tin oxide that includes silicon or silicon oxide, or zinc oxide)is preferably used for the second electrode 417.

The sealing substrate 404 is attached to the element substrate 410 withthe sealant 405; thus, a light-emitting element 418 is provided in thespace 407 enclosed by the element substrate 410, the sealing substrate404, and the sealant 405. Note that the space 407 may be filled withfiller such as an inert gas (e.g., nitrogen or argon) or with thesealant 405.

Note that as the sealant 405, an epoxy-based resin is preferably used.Such a material is desirably a material that transmits as littlemoisture or oxygen as possible. As a material used for the sealingsubstrate 404, a glass substrate, a quartz substrate, or a plasticsubstrate formed of FRP (fiberglass-reinforced plastics), PVF (polyvinylfluoride), polyester, acrylic, or the like can be used.

As described above, the active matrix light-emitting device having alight-emitting element of one embodiment of the present invention can beobtained.

Further, a light-emitting element of the present invention can be usedfor a passive matrix light-emitting device as well as the above activematrix light-emitting device. FIGS. 4A and 4B illustrate a perspectiveview and a cross-sectional view of a passive matrix light-emittingdevice using a light-emitting element of the present invention. Notethat FIG. 4A is a perspective view of the light-emitting device, andFIG. 4B is a cross-sectional view taken along line X-Y of FIG. 4A.

In FIGS. 4A and 4B, an EL layer 504 is provided between a firstelectrode 502 and a second electrode 503 over a substrate 501. An endportion of the first electrode 502 is covered with an insulating layer505. In addition, a partition layer 506 is provided over the insulatinglayer 505. The sidewalls of the partition layer 506 are aslope so that adistance between both the sidewalls is gradually narrowed toward thesurface of the substrate. In other words, a cross section taken alongthe direction of the short side of the partition layer 506 istrapezoidal, and the base (side facing in a direction parallel to theplane direction of the insulating layer 505 and being in contact withthe insulating layer 505) is shorter than the upper side (side facing inthe direction parallel to the plane direction of the insulating layer505 and not being in contact with the insulating layer 505). Byproviding of the partition layer 506 in such a manner, a defect of alight-emitting element due to static electricity or the like can beprevented.

Thus, the passive matrix light-emitting device having a light-emittingelement of one embodiment of the present invention can be obtained.

The light-emitting devices described in this embodiment (the activematrix light-emitting device and the passive matrix light-emittingdevice) are both formed using a light-emitting element of one embodimentof the present invention, thereby having low power consumption.

Note that this embodiment can be combined with any other embodiment asappropriate.

Embodiment 5

Embodiment 5 will give descriptions of electronic devices including alight-emitting device of one embodiment of the present inventiondescribed in Embodiment 4 as a part. Examples of the electronic devicesinclude cameras such as video cameras and digital cameras, goggle typedisplays, navigation systems, audio reproducing devices (e.g., car audiosystems and audio systems), computers, game machines, portableinformation terminals (e.g., mobile computers, cellular phones, portablegame machines, and electronic books), image reproducing devices in whicha recording medium is provided (specifically, devices that are capableof reproducing recording media such as digital versatile discs (DVDs)and provided with a display device that can display an image), and thelike. Specific examples of these electronic devices are illustrated inFIGS. 5A to 5D.

FIG. 5A illustrates a television set according to one embodiment of thepresent invention, which includes a housing 611, a supporting base 612,a display portion 613, speaker portions 614, video input terminals 615,and the like. In this television set, a light-emitting device of oneembodiment of the present invention can be applied to the displayportion 613. Since a light-emitting device of one embodiment of thepresent invention has low driving voltage, high current efficiency, anda long lifetime, by the application of the light-emitting device of oneembodiment of the present invention, a television set having highreliability and reduced power consumption can be obtained.

FIG. 5B illustrates a computer according to one embodiment of thepresent invention, which includes a main body 621, a housing 622, adisplay portion 623, a keyboard 624, an external connection port 625, apointing device 626, and the like. In this computer, the light-emittingdevice of the present invention can be applied to the display portion623. Since a light-emitting device of one embodiment of the presentinvention has low driving voltage, high current efficiency, and a longlifetime, by the application of the light-emitting device of oneembodiment of the present invention, a computer having high reliabilityand reduced power consumption can be obtained.

FIG. 5C illustrates a cellular phone of one embodiment of the presentinvention, which includes a main body 631, a housing 632, a displayportion 633, an audio input portion 634, an audio output portion 635,operation keys 636, an external connection port 637, an antenna 638, andthe like. In this cellular phone, the light-emitting device of thepresent invention can be applied to the display portion 633. Since alight-emitting device of one embodiment of the present invention has lowdriving voltage, high current efficiency, and a long lifetime, by theapplication of the light-emitting device of one embodiment of thepresent invention, a cellular phone having high reliability and reducedpower consumption can be obtained.

FIG. 5D illustrates a camera of one embodiment of the present invention,which includes a main body 641, a display portion 642, a housing 643, anexternal connection port 644, a remote control receiving portion 645, animage receiving portion 646, a battery 647, an audio input portion 648,operation keys 649, an eyepiece portion 650, and the like. In thiscamera, a light-emitting device of one embodiment of the presentinvention can be applied to the display portion 642. Since alight-emitting device of one embodiment of the present invention has lowdriving voltage, high current efficiency, and a long lifetime, by theapplication of the light-emitting device of one embodiment of thepresent invention, a camera having high reliability and reduced powerconsumption can be obtained.

As thus described, application range of a light-emitting device of oneembodiment of the present invention is quite wide, and thislight-emitting device can be applied to electronic devices of a varietyof fields. With use of a light-emitting device of one embodiment of thepresent invention, an electronic device having high reliability andreduced power consumption can be obtained.

Moreover, a light-emitting device of one embodiment of the presentinvention can be used as a lighting device. FIG. 6 illustrates anexample of a liquid crystal display device using a light-emitting deviceof one embodiment of the present invention as a backlight. The liquidcrystal display device illustrated in FIG. 6 includes a housing 701, aliquid crystal layer 702, a backlight 703, and a housing 704. The liquidcrystal layer 702 is electrically connected to a driver IC 705. Thelight-emitting device of one embodiment of the present invention is usedas the backlight 703, and a current is supplied to the backlight 703through a terminal 706.

By using a light-emitting device of one embodiment of the presentinvention as a backlight of a liquid crystal display device as describedabove, a backlight having reduced power consumption can be obtained.Moreover, since a light-emitting device of one embodiment of the presentinvention is a lighting device for planar light emission and theenlargement of the light-emitting device is possible, the area of thebacklight can also be made larger. Thus, a liquid crystal display devicehaving reduced power consumption and a large area can be obtained.

FIG. 7 illustrates an example in which a light-emitting device of oneembodiment of the present invention is used for a desk lamp which is alighting device. The desk lamp illustrated in FIG. 7 has a housing 801and a light source 802, and a light-emitting device of one embodiment ofthe present invention is used as the light source 802. Since thelight-emitting device of one embodiment of the present invention has lowdriving voltage, high current efficiency, and a long lifetime, by itsapplication, a desk lamp having high reliability and reduced powerconsumption can be obtained.

FIG. 8 illustrates an example in which a light-emitting device of oneembodiment of the present invention is used for an indoor lightingdevice 901. Since the light-emitting device of one embodiment of thepresent invention can have a larger area, it can be used as a lightingdevice having a large area. Further, since the light-emitting device ofone embodiment of the present invention has low driving voltage, highcurrent efficiency, and a long lifetime, by the application of thelight-emitting device of one embodiment of the present invention, alighting device having high reliability and reduced power consumptioncan be obtained. In a room where the light-emitting device of oneembodiment of the present invention is used as the indoor lightingdevice 901 as above, a television set 902 of one embodiment of thepresent invention as described referring to FIG. 5A can be installed sothat pubic broadcasting and movies can be watched.

Note that this embodiment can be combined with any other embodiment asappropriate.

Example 1 Synthesis Example 1

This example gives descriptions of a method of synthesizing2-[3-(dibenzothiophen-4-yl)phenyl]dibenzo[f,h]quinoxaline (abbreviation:2mDBTPDBq-II) represented by the following Structural Formula (101).

[Synthesis of 2mDBTPDBq-II]

A scheme for the synthesis of 2mDBTPDBq-II is illustrated in (C-1).

In a 2-L three-neck flask were put 5.3 g (20 mmol) of2-chlorodibenzo[f,h]quinoxaline, 6.1 g (20 mmol) of3-(dibenzothiophen-4-yl)phenylboronic acid, 460 mg (0.4 mmol) oftetrakis(triphenylphosphine)palladium(0), 300 mL of toluene, 20 mL ofethanol, and 20 mL of a 2M aqueous potassium carbonate solution. Thismixture was degassed by stirring under reduced pressure, and the air inthe flask was replaced with nitrogen. This mixture was stirred under anitrogen stream at 100° C. for 7.5 hours. After cooled to roomtemperature, the obtained mixture was filtered to give a whitesubstance. The substance obtained by the filtration was washed well withwater and ethanol in this order, and then dried. The obtained solid wasdissolved in about 600 mL of hot toluene, followed by suction filtrationthrough Celite (produced by Wako Pure Chemical Industries, Ltd., CatalogNo. 531-16855) and Florisil (produced by Wako Pure Chemical Industries,Ltd., Catalog No. 540-00135), whereby a clear colorless filtrate wasobtained. The obtained filtrate was concentrated and purified by silicagel column chromatography. The chromatography was carried out using hottoluene as a developing solvent. Acetone and ethanol were added to thesolid obtained here, followed by irradiation with ultrasonic waves.Then, the generated suspended solid was filtered and the obtained solidwas dried to give 7.85 g of a white powder in 80% yield, which was thesubstance to be produced.

The above produced substance was relatively soluble in hot toluene, butis a material that is easy to precipitate when cooled. Further, thesubstance was poorly soluble in other organic solvents such as acetoneand ethanol. Hence, the utilization of these different degrees ofsolubility resulted in a high-yield synthesis by a simple method asabove. Specifically, after the reaction finished, the mixture wasreturned to room temperature and the precipitated solid was collected byfiltration, whereby most impurities were able to be easily removed.Further, by the column chromatography with hot toluene as a developingsolvent, the produced substance, which is easy to precipitate, was ableto be readily purified.

By a train sublimation method, 4.0 g of the obtained white powder waspurified. In the purification, the white powder was heated at 300° C.under a pressure of 5.0 Pa with a flow rate of argon gas of 5 mL/min.After the purification, 3.5 g of a white powder was obtained in a yieldof 88%, which was the substance to be produced.

A nuclear magnetic resonance (NMR) method identified this compound as2-[3-(dibenzothiophen-4-yl)phenyl]dibenzo[f,h]quinoxaline (abbreviation:2mDBTPDBq-II), which was the substance to be produced.

¹H NMR data of the obtained substance are as follows: ¹H NMR (CDCl₃, 300MHz): δ (ppm)=7.45-7.52 (m, 2H), 7.59-7.65 (m, 2H), 7.71-7.91 (m, 7H),8.20-8.25 (m, 2H), 8.41 (d, J=7.8 Hz, 1H), 8.65 (d, J=7.5 Hz, 2H),8.77-8.78 (m, 1H), 9.23 (dd, J=7.2 Hz, 1.5 Hz, 1H), 9.42 (dd, J=7.8 Hz,1.5 Hz, 1H), 9.48 (s, 1H).

FIGS. 9A and 9B illustrate the ¹H NMR charts. Note that FIG. 9B is achart showing an enlarged part of FIG. 9A in the range of 7.0 ppm to10.0 ppm.

Further, FIG. 10A shows an absorption spectrum of a toluene solution of2mDBTPDBq-II, and FIG. 10B shows an emission spectrum thereof. FIG. 11Ashows an absorption spectrum of a thin film of 2mDBTPDBq-II, and FIG.11B shows an emission spectrum thereof. The absorption spectrum wasmeasured using an ultraviolet-visible spectrophotometer (V-550, producedby JASCO Corporation). The measurements were performed with samplesprepared in such a manner that the solution was put in a quartz cell andthe thin film was obtained by evaporation onto a quartz substrate. Theabsorption spectrum of the solution was obtained by subtracting theabsorption spectra of quartz and toluene from those of quartz and thesolution, and the absorption spectrum of the thin film was obtained bysubtracting the absorption spectrum of a quartz substrate from those ofthe quartz substrate and the thin film. In FIGS. 10A and 10B and FIGS.11A and 11B, the horizontal axis represents wavelength (nm) and thevertical axis represents intensity (arbitrary unit). In the case of thetoluene solution, an absorption peak was observed at around 375 nm, andemission wavelength peaks were 386 nm and 405 nm (at an excitationwavelength of 363 nm). In the case of the thin film, absorption peakswere observed at around 250 nm, 312 nm, 369 nm, and 385 nm, and anemission wavelength peak was 426 nm (at an excitation wavelength of 385nm).

Example 2 Synthesis Example 2

This example gives descriptions of a method of synthesizing2-[4-(3,6-diphenyl-9H-carbazol-9-yl)phenyl]dibenzo[f,h]quinoxaline(abbreviation: 2CzPDBq-III) represented by the following StructuralFormula (338).

[Synthesis of 2CzPDBq-III]

A scheme for the synthesis of 2CzPDBq-III is illustrated in (C-2).

In a 50-mL three-neck flask were put 0.6 g (2.3 mmol) of2-chlorodibenzo[f,h]quinoxaline, 1.1 g (2.5 mmol) of4-(3,6-diphenyl-9H-carbazol-9-yl)phenylboronic acid, 10 mL of toluene, 2mL of ethanol, and 3 mL of a 2M aqueous potassium carbonate solution.This mixture was degassed by stirring under reduced pressure, and theair in the flask was replaced with nitrogen. To this mixture was added89 mg (75 μmol) of tetrakis(triphenylphosphine)palladium(0). Thismixture was stirred under a nitrogen stream at 80° C. for 5 hours. Aftera predetermined time had elapsed, water was added to the obtainedmixture, and organic substances were extracted from the aqueous layerwith chloroform. The obtained solution of the extracted organicsubstances was combined with the organic layer, the mixture was washedwith saturated brine, and the organic layer was dried with magnesiumsulfate. The obtained mixture was gravity filtered, and the filtrate wasconcentrated to give a solid. The obtained solid was dissolved intoluene, and the toluene solution was suction filtered through Celite(produced by Wako Pure Chemical Industries, Ltd., Catalog No.531-16855), Florisil (produced by Wako Pure Chemical Industries, Ltd.,Catalog No. 540-00135), and alumina, and the filtrate was concentratedto give a solid. After methanol was added to this solid and the methanolsuspension was irradiated with ultrasonic waves, the solid was suctionfiltered to give a solid. This obtained solid was washed with toluene.The obtained solid was recrystallized from toluene, giving 1.0 g of ayellow powder in a yield of 65%, which was the substance to be produced.

By a train sublimation method, 0.97 g of the obtained yellow powder waspurified. In the purification, the yellow powder was heated at 350° C.under a pressure of 2.4 Pa with a flow rate of argon gas of 5 mL/min.After the purification, 0.92 g of a yellow powder was obtained in ayield of 95%, which was the substance to be produced.

A nuclear magnetic resonance (NMR) method identified this compound as2-[4-(3,6-diphenyl-9H-carbazol-9-yl)phenyl]dibenzo[f,h]quinoxaline(abbreviation: 2CzPDBq-III), which was the substance to be produced.

¹H NMR data of the obtained substance are as follows: ¹H NMR (CDCl₃, 300MHz): δ (ppm)=7.35 (t, J=7.2 Hz, 2H), 7.49 (t, J=7.2 Hz, 4H), 7.63 (d,J=8.1 Hz, 2H), 7.73-7.90 (m, 12H), 8.42 (d, J=1.5 Hz, 2H), 8.62-8.69 (m,4H), 9.25-9.28 (m, 1H), 9.45-9.48 (m, 1H), 9.50 (s, 1H).

FIGS. 12A and 12B illustrate the ¹H NMR charts. Note that FIG. 12B is achart showing an enlarged part of FIG. 12A in the range of 7.0 ppm to10.0 ppm.

Further, FIG. 13A shows an absorption spectrum of a toluene solution of2CzPDBq-III, and FIG. 13B shows an emission spectrum thereof. FIG. 14Ashows an absorption spectrum of a thin film of 2CzPDBq-III, and FIG. 14Bshows an emission spectrum thereof. The absorption spectrum was measuredusing an ultraviolet-visible spectrophotometer (V-550, produced by JASCOCorporation). The measurements were performed with samples prepared insuch a manner that the solution was put in a quartz cell and the thinfilm was obtained by evaporation onto a quartz substrate. The absorptionspectrum of the solution was obtained by subtracting the absorptionspectra of quartz and toluene from those of quartz and the solution, andthe absorption spectrum of the thin film was obtained by subtracting theabsorption spectrum of a quartz substrate from those of the quartzsubstrate and the thin film. In FIGS. 13A and 13B and FIGS. 14A and 14B,the horizontal axis represents wavelength (nm) and the vertical axisrepresents intensity (arbitrary unit). In the case of the toluenesolution, an absorption peak was observed at around 385 nm, and anemission wavelength peak was 436 nm (at an excitation wavelength of 385nm). In the case of the thin film, absorption peaks were observed ataround 267 nm, 307 nm, and 399 nm, and an emission wavelength peak was469 nm (at an excitation wavelength of 396 nm).

Example 3

In this example, a light-emitting element of one embodiment of thepresent invention will be described referring to FIG. 18. Chemicalformulae of materials used in this example are illustrated below.

Methods of fabricating Light-emitting Element 1, Light-emitting Element2, Reference Light-emitting Element 3, and Reference Light-emittingElement 4 of this example will be described below.

(Light-Emitting Element 1)

First, indium tin oxide containing silicon oxide (ITSO) was depositedover a glass substrate 1100 by a sputtering method, whereby a firstelectrode 1101 was formed. Note that its thickness was set to 110 nm andthe electrode area was set to 2 mm×2 mm. Here, the first electrode 1101is an electrode that functions as an anode of the light-emittingelement.

Next, as pretreatment for forming the light-emitting element over thesubstrate 1100, after washing of a surface of the substrate with waterand baking that was performed at 200° C. for one hour, UV ozonetreatment was performed for 370 seconds.

After that, the substrate was transferred into a vacuum evaporationapparatus where the pressure had been reduced to approximately 10⁻⁴ Pa,and subjected to vacuum baking at 170° C. for 30 minutes in a heatingchamber of the vacuum evaporation apparatus, and then the substrate 1100was cooled down for about 30 minutes.

Next, the substrate 1100 provided with the first electrode 1101 wasfixed to a substrate holder in a vacuum evaporation apparatus so that asurface on which the first electrode 1101 was provided faced downward.The pressure in the vacuum evaporation apparatus was reduced to about10⁻⁴ Pa. Then, by an evaporation method using resistance heating,4-phenyl-4′-(9-phenylfluoren-9-yl)triphenylamine (abbreviation: BPAFLP)and molybdenum(VI) oxide were co-evaporated to form a hole-injectionlayer 1111 over the first electrode 1101. The thickness of thehole-injection layer 1111 was set to 40 nm, and the weight ratio ofBPAFLP to molybdenum(VI) oxide was adjusted to 4:2(=BPAFLP:molybdenum(VI) oxide). Note that the co-evaporation methodrefers to an evaporation method in which evaporation is carried out froma plurality of evaporation sources at the same time in one treatmentchamber.

Next, a BPAFLP film was formed to a thickness of 20 nm over thehole-injection layer 1111, whereby a hole-transport layer 1112 wasformed.

Further,2-[4-(3,6-diphenyl-9H-carbazol-9-yl)phenyl]dibenzo[f,h]quinoxaline(abbreviation: 2CzPDBq-III) synthesized in Example 2,4-phenyl-4′-(9-phenyl-9H-carbazol-3-yl)triphenylamine (abbreviation:PCBA1BP), and(acetylacetonato)bis(3,5-dimethyl-2-phenylpyrazinato)iridium(III)(abbreviation: [ft(mppr-Me)₂(acac)]) were co-evaporated to form alight-emitting layer 1113 over the hole-transport layer 1112. The weightratio of 2CzPDBq-III to PCBA1BP and [Ir(mppr-Me)₂(acac)] was adjusted to1:0.15:0.06 (=2CzPDBq-III:PCBA1BP:[Ir(mppr-Me)₂(acac)]). The thicknessof the light-emitting layer 1113 was set to 40 nm.

Further, a 2CzPDBq-III film was formed to a thickness of 10 nm over thelight-emitting layer 1113, whereby a first electron-transport layer 1114a was formed.

Then, a bathophenanthroline (abbreviation: BPhen) film was formed to athickness of 20 nm over the first electron-transport layer 1114 a,whereby a second electron-transport layer 1114 b was formed.

Further, a lithium fluoride (LiF) film was formed to a thickness of 1 nmover the second electron-transport layer 1114 b by evaporation, wherebyan electron-injection layer 1115 was formed.

Lastly, an aluminum film was formed to a thickness of 200 nm byevaporation as a second electrode 1103 functioning as a cathode. Thus,Light-emitting Element 1 of this example was fabricated.

Note that, in the above evaporation process, evaporation was allperformed by a resistance heating method.

(Light-Emitting Element 2)

The light-emitting layer 1113 of Light-emitting Element 2 was formed byco-evaporation of2-[3-(dibenzothiophen-4-yl)phenyl]dibenzo[f,h]quinoxaline (abbreviation:2mDBTPDBq-II) synthesized in Example 1, PCBA1BP, and[Ir(mppr-Me)₂(acac)]. The weight ratio of 2mDBTPDBq-II to PCBA1BP and[Ir(mppr-Me)₂(acac)] was adjusted to 1:0.25:0.06 (=2mDBTPDBq-II:PCBA1BP: [Ir(mppr-Me)₂(acac)]). The thickness of the light-emittinglayer 1113 was set to 40 nm.

The first electron-transport layer 1114 a of Light-emitting Element 2was formed with a 10-nm-thick 2mDBTPDBq-II film. The components otherthan the light-emitting layer 1113 and the first electron-transportlayer 1114 a were formed in the same manner as those of Light-emittingElement 1.

(Reference Light-Emitting Element 3)

The light-emitting layer 1113 of Reference Light-emitting Element 3 wasformed by co-evaporation of2-[4-(3,6-diphenyl-9H-carbazol-9-yl)phenyl]-3-phenylquinoxaline(abbreviation: Cz1PQ-III), PCBA1BP, and [Ir(mppr-Me)₂(acac)]. The weightratio of Cz1PQ-III to PCBA1BP and [Ir(mppr-Me)₂(acac)] was adjusted to1:0.3:0.06 (=Cz1PQ-III:PCBA1BP:[Ir(mppr-Me)₂(acac)]). The thickness ofthe light-emitting layer 1113 was set to 40 nm.

The first electron-transport layer 1114 a of Reference Light-emittingElement 3 was formed with a 10-nm-thick Cz1PQ-III film. The componentsother than the light-emitting layer 1113 and the firstelectron-transport layer 1114 a were formed in the same manner as thoseof Light-emitting Element 1.

(Reference Light-Emitting Element 4)

The light-emitting layer 1113 of Reference Light-emitting Element 4 wasformed by co-evaporation of4-[3-(triphenylen-2-yl)phenyl]dibenzothiophene (abbreviation:mDBTPTp-II), PCBA1BP, and [Ir(mppr-Me)₂(acac)]. The weight ratio ofmDBTPTp-II to PCBA1BP and [Ir(mppr-Me)₂(acac)] was adjusted to1:0.15:0.06 (=mDBTPTp-II:PCBA1BP:[Ir(mppr-Me)₂(acac)]). The thickness ofthe light-emitting layer 1113 was set to 40 nm.

The first electron-transport layer 1114 a of Reference Light-emittingElement 4 was formed with a 10-nm-thick mDBTPTp-II film. The componentsother than the light-emitting layer 1113 and the firstelectron-transport layer 1114 a were formed in the same manner as thoseof Light-emitting Element 1.

Table 1 shows element structures of Light-emitting Elements 1 and 2 andReference Light-emitting Elements 3 and 4 obtained as described above.

TABLE 1 First Second Hole- Hole- Light- electron- electron- Electron-First injection transport emitting transport transport injection Secondelectrode layer layer layer layer layer layer electrode Light- ITSOBPAFLP: BPAFLP 2CzPDBq-III: 2CzPDBq-III BPhen LiF Al emitting 110 nmMoOx 20 nm PCBA1BP: 10 nm 20 nm 1 nm 200 nm element 1 (=4:2)[Ir(mppr-Me)₂(acac)] 40 nm (=1:0.15:0.06) 40 nm Light- ITSO BPAFLP:BPAFLP 2mDBTPDBq- II: 2mDBTPDBq-II BPhen LiF Al emitting 110 nm MoOx 20nm PCBA1BP: 10 nm 20 nm 1 nm 200 nm element 2 (=4:2)[Ir(mppr-Me)₂(acac)] 40 nm (=1:0.25:0.06) 40 nm Reference ITSO BPAFLP:BPAFLP Cz1PQ-III: Cz1PQ-III BPhen LiF Al light- 110 nm MoOx 20 nmPCBA1BP: 10 nm 20 nm 1 nm 200 nm emitting (=4:2) [Ir(mppr-Me)₂(acac)]element 3 40 nm (=1:0.3:0.06) 40 nm Reference ITSO BPAFLP: BPAFLPmDBTPTp- II: mDBTPTp- II BPhen LiF Al light- 110 nm MoOx 20 nm PCBA1BP:10 nm 20 nm 1 nm 200 nm emitting (=4:2) [Ir(mppr-Me)₂(acac)] element 440 nm (=1:0.15:0.06) 40 nm

In a glove box containing a nitrogen atmosphere, Light-emitting Elements1 and 2 and Reference Light-emitting Elements 3 and 4 were sealed with aglass substrate so as not to be exposed to air. Then, operationcharacteristics of these elements were measured. Note that themeasurements were carried out at room temperature (in the atmospherekept at 25° C.).

FIG. 15 shows the voltage vs. luminance characteristics ofLight-emitting Elements 1 and 2 and Reference Light-emitting Elements 3and 4. In FIG. 15, the horizontal axis represents voltage (V) and thevertical axis represents luminance (cd/m²). In addition, FIG. 16 showsthe luminance vs. current efficiency characteristics of the elements. InFIG. 16, the horizontal axis represents luminance (cd/m²) and thevertical axis represents current efficiency (cd/A). Further, Table 2shows the voltage (V), current density (mA/cm²), CIE chromaticitycoordinates (x, y), current efficiency (cd/A), and external quantumefficiency (%) of each light-emitting element at a luminance of around1000 cd/m².

TABLE 2 External Current Chroma- Chroma- Current quantum Voltage densityticity ticity Luminance efficiency efficiency (V) (mA/cm²) x y (cd/m²)(cd/A) (%) Light- 2.8 1.3 0.54 0.46 850 65 24 emitting element 1 Light-2.9 1.4 0.54 0.46 860 64 23 emitting element 2 Reference 3.2 2.0 0.530.46 1200 61 22 Light- emitting element 3 Reference 4.4 1.9 0.55 0.45970 52 18 Light- emitting element 4

As shown in Table 2, the CIE chromaticity coordinates (x, y) ofLight-emitting Element 1 were (0.54, 0.46) at a luminance of 850 cd/m².The CIE chromaticity coordinates (x, y) of Light-emitting Element 2 were(0.54, 0.46) at a luminance of 860 cd/m². The CIE chromaticitycoordinates (x, y) of Reference Light-emitting Element 3 were (0.53,0.46) at a luminance of 1200 cd/m². The CIE chromaticity coordinates (x,y) of Reference Light-emitting Element 4 were (0.55, 0.45) at aluminance of 970 cd/m². It is found that all these light-emittingelements exhibited light emission from [Ir(mppr-Me)₂(acac)].

FIG. 15 reveals that Light-emitting Elements 1 and 2 each have lowdriving voltage and high current efficiency. A structural difference inthe compounds each used as a host material of a light-emitting layerbetween Light-emitting Element 2 and Reference Light-emitting Element 4is that a dibenzo[f,h]quinoxaline skeleton is included in Light-emittingElement 2 while a triphenylene skeleton is included in ReferenceLight-emitting Element 4. Which of a dibenzo[f,h]quinoxaline skeleton ora triphenylene skeleton was included made a differences in voltage vs.luminance characteristics and luminance vs. current efficiencycharacteristics between Light-emitting Element 2 and ReferenceLight-emitting Element 4. It is thus confirmed that, like a heterocycliccompound of one embodiment of the present invention, a compound having adibenzo[f,h]quinoxaline skeleton is effective in realizing high voltagevs. luminance characteristics and high luminance vs. current efficiencycharacteristics.

Next, Light-emitting Elements 1 and 2 and Reference Light-emittingElements 3 and 4 were subjected to reliability tests. Results of thereliability tests are shown in FIG. 17. In FIG. 17, the vertical axisrepresents normalized luminance (%) with an initial luminance of 100%,and the horizontal axis represents driving time (h) of the elements. Inthe reliability tests, the light-emitting elements of this example weredriven under the conditions where the current density was constant andthe initial luminance was 5000 cd/m². FIG. 17 shows that Light-emittingElement 1 kept 82% of the initial luminance after driving for 230 hoursand Light-emitting Element 2 kept 89% of the initial luminance afterdriving for 230 hours. The luminance of Reference Light-emitting Element3 decreases to 62% of the initial luminance after 210 hours, and theluminance of Reference Light-emitting Element 4 decreases to 69% of theinitial luminance after 210 hours. These results of the reliabilitytests revealed that Light-emitting Elements 1 and 2 each had a longlifetime. Note that, from these results, when the initial luminance is5000 cd/m², the luminance half life of Light-emitting Element 2, whoselifetime was the longest, is estimated at about 6000 hours. When theinitial luminance is changed to 1000 cd/m², which is of practical use,this luminance half life corresponds to 150000 hours, indicating thatthe lifetime is extremely long.

A dibenzo[f,h]quinoxaline skeleton is included in Light-emitting Element1 while a quinoxaline skeleton is included in Reference Light-emittingElement 3. Whether a dibenzo[f,h]quinoxaline skeleton is included or notmade a difference in the results of the reliability tests betweenLight-emitting Element 1 and Reference Light-emitting Element 3. It isthus confirmed that, like a heterocyclic compound of one embodiment ofthe present invention, having a dibenzo[f,h]quinoxaline skeleton iseffective in realizing a light-emitting element with much higherreliability.

As described above, by the use of 2mDBTPDBq-II produced in Example 1 and2CzPDBq-III produced in Example 2, each as a host material of alight-emitting layer, the light-emitting elements having a long lifetimewere able to be fabricated.

Example 4 Synthesis Example 3

This example gives descriptions of a method of synthesizing2-[4-(dibenzothiophen-4-yl)phenyl]dibenzo[f,h]quinoxaline (abbreviation:2DBTPDBq-II) represented by the following Structural Formula (100).

[Synthesis of 2DBTPDBq-II]

A scheme for the synthesis of 2DBTPDBq-II is illustrated in (C-3).

In a 100-mL three-neck flask were put 2.7 g (10 mmol) of2-chlorodibenzo[f,h]quinoxaline, 3.4 g (11 mmol) of4-(dibenzothiophen-4-yl)phenylboronic acid, 80 mL of toluene, 8.0 mL ofethanol, and 15 mL of a 2M aqueous potassium carbonate solution. Themixture was degassed by stirring under reduced pressure, and the air inthe flask was replaced with nitrogen. To this mixture was added 0.24 mg(0.20 mmol) of tetrakis(triphenylphosphine)palladium(0). This mixturewas stirred under a nitrogen stream at 80° C. for 24 hours. After apredetermined time had elapsed, the precipitated solid was suctionfiltered to give a solid. Ethanol was added to this solid, followed byirradiation with ultrasonic waves. The solid was suction filtered togive a solid. The obtained solid was dissolved in toluene, and thetoluene solution was suction filtered through Celite (produced by WakoPure Chemical Industries, Ltd., Catalog No. 531-16855) and alumina, andthe filtrate was concentrated to give a solid. This solid wasrecrystallized from toluene to give 3.2 g of a yellow powder in 65%yield.

By a train sublimation method, 1.3 g of the obtained yellow powder waspurified. In the purification, the yellow powder was heated at 310° C.under a pressure of 3.0 Pa with a flow rate of argon gas of 5 mL/min.After the purification, 1.1 g of a yellow powder was obtained in a yieldof 85%, which was the substance to be produced.

A nuclear magnetic resonance (NMR) method identified this compound as2-[4-(dibenzothiophen-4-yl)phenyl]dibenzo[f,h]quinoxaline (abbreviation:2DBTPDBq-II), which was the substance to be produced.

¹H NMR data of the obtained substance are as follows: ¹H NMR (CDCl₃, 300MHz): δ=7.50-7.53 (m, 2H), 7.62-7.65 (m, 2H), 7.80-7.91 (m, 5H), 8.03(d, J=8.4 Hz, 2H), 8.23-8.26 (m, 2H), 8.56 (d, J=8.1 Hz, 2H), 8.70 (d,J=7.8 Hz, 2H), 9.30 (dd, J=7.8 Hz, 1.8 Hz, 1H), 9.49-9.51 (m, 2H).

FIGS. 19A and 19B illustrate the ¹H NMR charts. Note that FIG. 19B is achart showing an enlarged part of FIG. 19A in the range of 7.0 ppm to10.0 ppm.

Further, FIG. 20A shows an absorption spectrum of a toluene solution of2DBTPDBq-II, and FIG. 20B shows an emission spectrum thereof. FIG. 21Ashows an absorption spectrum of a thin film of 2DBTPDBq-II, and FIG. 21Bshows an emission spectrum thereof. The absorption spectrum was measuredusing an ultraviolet-visible spectrophotometer (V-550, produced by JASCOCorporation). The measurements were performed with samples prepared insuch a manner that the solution was put in a quartz cell and the thinfilm was obtained by evaporation onto a quartz substrate. The absorptionspectrum of the solution was obtained by subtracting the absorptionspectra of quartz and toluene from those of quartz and the solution, andthe absorption spectrum of the thin film was obtained by subtracting theabsorption spectrum of a quartz substrate from those of the quartzsubstrate and the thin film. In FIGS. 20A and 20B and FIGS. 21A and 21B,the horizontal axis represents wavelength (nm) and the vertical axisrepresents intensity (arbitrary unit). In the case of the toluenesolution, absorption peaks were observed at around 294 nm, 309 nm, and375 nm, and emission wavelength peaks were 398 nm and 416 nm (at anexcitation wavelength of 350 nm). In the case of the thin film,absorption peaks were observed at around 241 nm, 262 nm, 316 nm, and 386nm, and an emission wavelength peak was 468 nm (at an excitationwavelength of 386 nm).

Example 5 Synthesis Example 4

This example gives descriptions of a method of synthesizing2-[3′-(dibenzothiophen-4-yl)biphenyl-3-yl]dibenzo[f,h]quinoxaline(abbreviation: 2mDBTBPDBq-II) represented by the following StructuralFormula (109).

[Synthesis of 2mDBTBPDBq-II]

A scheme for the synthesis of 2mDBTBPDBq-II is illustrated in (C-4).

In a 200-mL three-neck flask were put 0.83 g (3.2 mmol) of2-chlorodibenzo[f,h]quinoxaline, 1.3 g (3.5 mmol) of3′-(dibenzothiophen-4-yl)-3-biphenylboronic acid, 40 mL of toluene, 4 mLof ethanol, and 5 mL of a 2M aqueous potassium carbonate solution. Thismixture was degassed by stirring under reduced pressure, and the air inthe flask was replaced with nitrogen. To this mixture was added 80 mg(70 μmol) of tetrakis(triphenylphosphine)palladium(0). This mixture wasstirred under a nitrogen stream at 80° C. for 16 hours. After apredetermined time had elapsed, the precipitated solid was separated byfiltration to give a yellow solid. Ethanol was added to this solid,followed by irradiation with ultrasonic waves. The solid was suctionfiltered to give a solid. The obtained solid was dissolved in toluene,and the toluene solution was suction filtered through alumina and Celite(produced by Wako Pure Chemical Industries, Ltd., Catalog No.531-16855), and the filtrate was concentrated to give a yellow solid.Further, this solid was recrystallized from toluene to give 1.1 g of ayellow powder in 57% yield.

By a train sublimation method, 1.1 g of the obtained yellow powder waspurified. In the purification, the yellow powder was heated at 300° C.under a pressure of 6.2 Pa with a flow rate of argon gas of 15 mL/min.After the purification, 0.80 g of a yellow powder was obtained in ayield of 73%, which was the substance to be produced.

A nuclear magnetic resonance (NMR) method identified this compound as2-[3′-(dibenzothiophen-4-yl)biphenyl-3-yl]dibenzo[f,h]quinoxaline(abbreviation: 2mDBTBPDBq-II), which was the substance to be produced.

¹H NMR data of the obtained substance are as follows: ¹H NMR (CDCl₃, 300MHz): δ=7.46-7.50 (m, 2H), 7.61 (d, J=4.5 Hz, 2H), 7.67-7.89 (m, 10H),8.17-8.24 (m, 3H), 8.35 (d, J=8.1 Hz, 1H), 8.65-8.70 (m, 3H), 9.24-9.27(m, 1H), 9.44-9.48 (m, 2H).

FIGS. 22A and 22B illustrate the ¹H NMR charts. Note that FIG. 22B is achart showing an enlarged part of FIG. 22A in the range of 7.0 ppm to10.0 ppm.

Further, FIG. 23A shows an absorption spectrum of a toluene solution of2mDBTBPDBq-II, and FIG. 23B shows an emission spectrum thereof. FIG. 24Ashows an absorption spectrum of a thin film of 2mDBTBPDBq-II, and FIG.24B shows an emission spectrum thereof. The absorption spectrum wasmeasured using an ultraviolet-visible spectrophotometer (V-550, producedby JASCO Corporation). The measurements were performed with samplesprepared in such a manner that the solution was put in a quartz cell andthe thin film was obtained by evaporation onto a quartz substrate. Theabsorption spectrum of the solution was obtained by subtracting theabsorption spectra of quartz and toluene from those of quartz and thesolution, and the absorption spectrum of the thin film was obtained bysubtracting the absorption spectrum of a quartz substrate from those ofthe quartz substrate and the thin film. In FIGS. 23A and 23B and FIGS.24A and 24B, the horizontal axis represents wavelength (nm) and thevertical axis represents intensity (arbitrary unit). In the case of thetoluene solution, absorption peaks were observed at around 361 nm and374 nm, and emission wavelength peaks were 385 nm and 405 nm (at anexcitation wavelength of 363 nm). In the case of the thin film,absorption peaks were observed at around 207 nm, 250 nm, 313 nm, 332 nm,368 nm, and 384 nm, and an emission wavelength peak was 428 nm (at anexcitation wavelength of 383 nm).

Example 6 Synthesis Example 5

This example gives descriptions of a method of synthesizing2-[3-(2,8-diphenyldibenzothiophen-4-yl)phenyl]dibenzo[f,h]quinoxaline(abbreviation: 2mDBTPDBq-III) represented by the following StructuralFormula (116).

[Synthesis of 2mDBTPDBq-III]

A scheme for the synthesis of 2mDBTPDBq-III is illustrated in (C-5).

In a 100-mL three-neck flask were put 0.40 g (1.5 mmol) of2-chlorodibenzo[f,h]quinoxaline, 0.68 g (1.5 mmol) of3-(2,8-diphenyldibenzothiophen-4-yl)phenylboronic acid, 15 mL oftoluene, 2.0 mL of ethanol, and 1.5 mL of a 2M aqueous potassiumcarbonate solution. This mixture was degassed by stirring under reducedpressure, and the air in the flask was replaced with nitrogen. To thismixture was added 51 mg (43 μmol) oftetrakis(triphenylphosphine)palladium(0). This mixture was stirred undera nitrogen stream at 80° C. for 4 hours. After a predetermined time hadelapsed, water was added to the obtained mixture, and organic substanceswere extracted from the aqueous layer with toluene. The obtainedsolution of the extracted organic substances was combined with theorganic layer, the mixture was washed with saturated brine, and theorganic layer was dried with magnesium sulfate. The obtained mixture wasgravity filtered, and the filtrate was concentrated to give a solid. Theobtained solid was dissolved in toluene, and the toluene solution wassuction filtered through alumina, Florisil (produced by Wako PureChemical Industries, Ltd., Catalog No. 540-00135), and Celite (producedby Wako Pure Chemical Industries, Ltd., Catalog No. 531-16855), and theobtained filtrate was concentrated to give a solid. The obtained solidwas washed with toluene, and added to methanol, and the methanolsuspension was irradiated with ultrasonic waves. A solid was collectedby suction filtration to give 0.60 g of a white powder in 61% yield,which was the substance to be produced.

By a train sublimation method, 0.59 g of the obtained white powder waspurified. In the purification, the white powder was heated at 330° C.under a pressure of 2.7 Pa with a flow rate of argon gas of 5 mL/min.After the purification, 0.54 g of a white powder was obtained in a yieldof 90%, which was the substance to be produced.

A nuclear magnetic resonance (NMR) method identified this compound as2-[3-(2,8-diphenyldibenzothiophen-4-yl)phenyl]dibenzo[f,h]quinoxaline(abbreviation: 2mDBTPDBq-III), which was the substance to be produced.

¹H NMR data of the obtained substance are as follows: ¹H NMR (CDCl₃, 300MHz): δ=7.37-7.55 (m, 6H), 7.73-7.84 (m, 10H), 7.90-7.98 (m, 3H),8.44-8.48 (m, 3H), 8.65 (dd, J=7.8 Hz, 1.5 Hz, 2H), 8.84-8.85 (m, 1H),9.27 (dd, J=7.2 Hz, 2.7 Hz, 1H), 9.46 (dd, J=7.8 Hz, 2.1 Hz, 1H), 9.51(s, 1H).

FIGS. 25A and 25B illustrate the ¹H NMR charts. Note that FIG. 25B is achart showing an enlarged part of FIG. 25A in the range of 7.0 ppm to10.0 ppm.

Further, FIG. 26A shows an absorption spectrum of a toluene solution of2mDBTPDBq-III, and FIG. 26B shows an emission spectrum thereof. FIG. 27Ashows an absorption spectrum of a thin film of 2mDBTPDBq-III, and FIG.27B shows an emission spectrum thereof. The absorption spectrum wasmeasured using an ultraviolet-visible spectrophotometer (V-550, producedby JASCO Corporation). The measurements were performed with samplesprepared in such a manner that the solution was put in a quartz cell andthe thin film was obtained by evaporation onto a quartz substrate. Theabsorption spectrum of the solution was obtained by subtracting theabsorption spectra of quartz and toluene from those of quartz and thesolution, and the absorption spectrum of the thin film was obtained bysubtracting the absorption spectrum of a quartz substrate from those ofthe quartz substrate and the thin film. In FIGS. 26A and 26B and FIGS.27A and 27B, the horizontal axis represents wavelength (nm) and thevertical axis represents intensity (arbitrary unit). In the case of thetoluene solution, absorption peaks were observed at around 281 nm, 297nm, 359 nm, and 374 nm, and emission wavelength peaks were 386 nm and405 nm (at an excitation wavelength of 375 nm). In the case of the thinfilm, absorption peaks were observed at around 266 nm, 302 nm, 366 nm,and 383 nm, and an emission wavelength peak was 462 nm (at an excitationwavelength of 383 nm).

Example 7 Synthesis Example 6

This example gives descriptions of a method of synthesizing2-[3-(dibenzothiophen-4-yl)phenyl]-3-phenyldibenzo[f,h]quinoxaline(abbreviation: 3Ph-2mDBTPDBq-II) represented by the following StructuralFormula (142).

[Synthesis of 3Ph-2mDBTPDBq-II]

A scheme for the synthesis of 3Ph-2mDBTPDBq-II is illustrated in (C-6).

In a 100-mL three-neck flask were put 1.2 g (2.5 mmol) of2-(3-bromophenyl)-3-phenyldibenzo[f,h]quinoxaline, 0.63 g (2.8 mmol) ofdibenzothiophene-4-boronic acid, 0.12 g (0.39 mmol) oftri(ortho-tolyl)phosphine, 25 mL of toluene, 5.0 mL of ethanol, and 3.0mL of a 2M aqueous potassium carbonate solution. This mixture wasdegassed by stirring under reduced pressure, and the air in the flaskwas replaced with nitrogen. To this mixture was added 40 mg (0.18 mmol)of palladium(II) acetate. This mixture was stirred under a nitrogenstream at 80° C. for 7 hours. After a predetermined time had elapsed,water was added to the obtained mixture, and organic substances wereextracted from the aqueous layer with toluene. The obtained solution ofthe extracted organic substances was combined with the organic layer,the mixture was washed with a saturated aqueous solution of sodiumhydrogen carbonate and saturated brine, and the organic layer was driedwith magnesium sulfate. The obtained mixture was gravity filtered, andthe filtrate was concentrated to give a solid. The obtained solid waspurified twice by silica gel column chromatography (with a developingsolvent of toluene and hexane in a ratio of 1:1). Further,recrystallization from toluene and methanol gave 0.65 g of a whitepowder in 46% yield, which was the substance to be produced.

By a train sublimation method, 0.62 g of the obtained white powder waspurified. In the purification, the white powder was heated at 285° C.under a pressure of 2.5 Pa with a flow rate of argon gas of 5 mL/min.After the purification, 0.54 g of a white powder was obtained in a yieldof 87%, which was the substance to be produced.

A nuclear magnetic resonance (NMR) method identified this compound as2-[3-(dibenzothiophen-4-yl)phenyl]-3-phenyldibenzo[f,h]quinoxaline(abbreviation: 3Ph-2mDBTPDBq-II), which was the substance to beproduced.

¹H NMR data of the obtained substance are as follows: ¹H NMR (CDCl₃, 300MHz): δ=7.33 (d, J=7.8 Hz, 1H), 7.44-7.60 (m, 7H), 7.72-7.85 (m, 9H),8.10-8.20 (m, 3H), 8.65 (d, J=7.8 Hz, 2H), 9.36 (td, J=7.8 Hz, 1.5 Hz,2H).

FIGS. 28A and 28B illustrate the ¹H NMR charts. Note that FIG. 28B is achart showing an enlarged part of FIG. 28A in the range of 7.0 ppm to10.0 ppm.

Further, FIG. 29A shows an absorption spectrum of a toluene solution of3Ph-2mDBTPDBq-II, and FIG. 29B shows an emission spectrum thereof. FIG.30A shows an absorption spectrum of a thin film of 3Ph-2mDBTPDBq-II, andFIG. 30B shows an emission spectrum thereof. The absorption spectrum wasmeasured using an ultraviolet-visible spectrophotometer (V-550, producedby JASCO Corporation). The measurements were performed with samplesprepared in such a manner that the solution was put in a quartz cell andthe thin film was obtained by evaporation onto a quartz substrate. Theabsorption spectrum of the solution was obtained by subtracting theabsorption spectra of quartz and toluene from those of quartz and thesolution, and the absorption spectrum of the thin film was obtained bysubtracting the absorption spectrum of a quartz substrate from those ofthe quartz substrate and the thin film. In FIGS. 29A and 29B and FIGS.30A and 30B, the horizontal axis represents wavelength (nm) and thevertical axis represents intensity (arbitrary unit). In the case of thetoluene solution, absorption peaks were observed at around 303 nm and377 nm, and an emission wavelength peak was 406 nm (at an excitationwavelength of 378 nm). In the case of the thin film, absorption peakswere observed at around 212 nm, 246 nm, 265 nm, 322 nm, 370 nm, and 385nm, and an emission wavelength peak was 416 nm (at an excitationwavelength of 385 nm).

Example 8 Synthesis Example 7

This example gives descriptions of a method of synthesizing2-[3-(dibenzofuran-4-yl)phenyl]dibenzo[f,h]quinoxaline (abbreviation:2mDBFPDBq-II) represented by the following Structural Formula (201).

[Synthesis of 2mDBFPDBq-II]

A scheme for the synthesis of 2mDBFPDBq-II is illustrated in (C-7).

In a 200-mL three-neck flask were put 1.0 g (3.8 mmol) of2-chlorodibenzo[f,h]quinoxaline, 1.2 g (4.2 mmol) of3-(dibenzofuran-4-yl)phenylboronic acid, 50 mL of toluene, 5.0 mL ofethanol, and 5.0 mL of a 2M aqueous potassium carbonate solution. Thismixture was degassed by stirring under reduced pressure, and the air inthe flask was replaced with nitrogen. To this mixture was added 0.10 mg(0.10 mmol) of tetrakis(triphenylphosphine)palladium(0). This mixturewas stirred at 80° C. for 8 hours under a nitrogen stream. After apredetermined time had elapsed, the precipitated solid was separated byfiltration to give a white solid. Further, water and toluene were addedto the filtrate, and organic substances were extracted from the aqueouslayer of the obtained filtrate with toluene. The solution of theextracted organic substances was combined with the organic layer, themixture was washed with a saturated aqueous solution of sodium hydrogencarbonate and saturated brine, followed by drying with magnesiumsulfate. The obtained mixture was gravity filtered, and then thefiltrate was concentrated to give a brown solid. The obtained solidswere combined, the obtained solids were dissolved in toluene, and thetoluene solution was suction filtered through alumina and Celite(produced by Wako Pure Chemical Industries, Ltd., Catalog No.531-16855). The obtained filtrate was concentrated to give a whitesolid. This solid was purified by silica gel column chromatography (witha developing solvent of toluene and hexane in a ratio of 1:10). Theobtained fractions were concentrated to give a yellow powder. Further,this solid was recrystallized from toluene to give 0.68 g of a yellowpowder in 33% yield, which was the substance to be produced.

By a train sublimation method, 0.68 g of the obtained yellow powder waspurified. In the purification, the yellow powder was heated at 280° C.under a pressure of 2.2 Pa with a flow rate of argon gas of 10 mL/min.After the purification, 0.43 g of a yellow powder was obtained in ayield of 67%, which was the substance to be produced.

A nuclear magnetic resonance (NMR) method identified this compound as2-[3-(dibenzofuran-4-yl)phenyl]dibenzo[f,h]quinoxaline (abbreviation:2mDBFPDBq-II), which was the substance to be produced.

¹H NMR data of the obtained substance are as follows: ¹H NMR (CDCl₃, 300MHz): δ=7.41 (t, J=7.8 Hz, 1H), 7.49-7.61 (m, 2H), 7.68 (d, J=8.4 Hz,1H), 7.76-7.84 (m, 6H), 8.02-8.10 (m, 3H), 8.41 (d, J=7.8 Hz, 1H), 8.67(d, J=7.8 Hz, 2H), 8.96-8.97 (m, 1H), 9.25-9.28 (m, 1H), 9.47-9.51 (m,2H).

FIGS. 31A and 31B illustrate the ¹H NMR charts. Note that FIG. 31B is achart showing an enlarged part of FIG. 31A in the range of 7.0 ppm to10.0 ppm.

Further, FIG. 32A shows an absorption spectrum of a toluene solution of2mDBFPDBq-II, and FIG. 32B shows an emission spectrum thereof. FIG. 33Ashows an absorption spectrum of a thin film of 2mDBFPDBq-II, and FIG.33B shows an emission spectrum thereof. The absorption spectrum wasmeasured using an ultraviolet-visible spectrophotometer (V-550, producedby JASCO Corporation). The measurements were performed with samplesprepared in such a manner that the solution was put in a quartz cell andthe thin film was obtained by evaporation onto a quartz substrate. Theabsorption spectrum of the solution was obtained by subtracting theabsorption spectra of quartz and toluene from those of quartz and thesolution, and the absorption spectrum of the thin film was obtained bysubtracting the absorption spectrum of a quartz substrate from those ofthe quartz substrate and the thin film. In FIGS. 32A and 32B and FIGS.33A and 33B, the horizontal axis represents wavelength (nm) and thevertical axis represents intensity (arbitrary unit). In the case of thetoluene solution, absorption peaks were observed at around 361 nm and374 nm, and emission wavelength peaks were 386 nm and 403 nm (at anexcitation wavelength of 374 nm). In the case of the thin film,absorption peaks were observed at around 207 nm, 260 nm, 304 nm, 369 nm,and 384 nm, and emission wavelength peaks were 425 nm and 575 nm (at anexcitation wavelength of 382 nm).

Example 9 Synthesis Example 8

This example gives descriptions of a method of synthesizing2-[3′-(9H-carbazol-9-yl)biphenyl-3-yl]dibenzo[f,h]quinoxaline(abbreviation: 2mCzBPDBq) represented by the following StructuralFormula (309).

[Synthesis of 2mCzBPDBq]

A scheme for the synthesis of 2mCzBPDBq is illustrated in (C-8).

In a 200-mL three-neck flask were put 1.0 g (4.0 mmol) of2-chlorodibenzo[f,h]quinoxaline, 1.6 g (4.4 mmol) of3′-(9H-carbazol-9-yl)-3-biphenylboronic acid, 50 mL of toluene, 5 mL ofethanol, and 6.0 mL of a 2M aqueous potassium carbonate solution. Thismixture was degassed by stirring under reduced pressure, and the air inthe flask was replaced with nitrogen. To this mixture was added 0.10 g(90 μmol) of tetrakis(triphenylphosphine)palladium(0). This mixture wasstirred under a nitrogen stream at 80° C. for 16 hours. After apredetermined time had elapsed, water was added to this mixture, andorganic substances were extracted from the aqueous layer of the obtainedfiltrate with toluene. The solution of the extracted organic substanceswas combined with the organic layer, the mixture was washed with asaturated aqueous solution of sodium hydrogen carbonate and saturatedbrine, followed by drying with magnesium sulfate. The obtained mixturewas gravity filtered, and then the filtrate was concentrated to give asolid. This solid was purified by silica gel column chromatography (witha developing solvent of toluene and hexane in a ratio of 1:3). Theobtained fractions were concentrated to give a solid. Further,recrystallization from toluene gave 0.32 g of a white powder in 15%yield.

By a train sublimation method, 0.32 g of the obtained white powder waspurified. In the purification, the white powder was heated at 300° C.under a pressure of 5.1 Pa with a flow rate of argon gas of 15 mL/min.After the purification, 0.12 g of a white powder was obtained in a yieldof 38%, which was the substance to be produced.

A nuclear magnetic resonance (NMR) method identified this compound as2-[3′-(9H-carbazol-9-yl)biphenyl-3-yl]dibenzo[f,h]quinoxaline(abbreviation: 2mCzBPDBq), which was the substance to be produced.

¹H NMR data of the obtained substance are as follows: ¹H NMR (CDCl₃, 300MHz): δ=7.26-7.35 (m, 2H), 7.43-7.49 (m, 2H), 7.56 (d, J=8.4 Hz, 2H),7.61-7.88 (m, 9H), 7.97-7.99 (m, 1H), 8.19 (d, J=7.8 Hz, 2H), 8.33-8.36(m, 1H), 8.65-8.67 (m, 3H), 9.25 (dd, J=7.8 Hz, 1.8 Hz, 1H), 9.41 (dd,J=7.8 Hz, 1.5 Hz, 1H), 9.45 (s, 1H).

FIGS. 34A and 34B illustrate the ¹H NMR charts. Note that FIG. 34B is achart showing an enlarged part of FIG. 34A in the range of 7.0 ppm to10.0 ppm.

Further, FIG. 35A shows an absorption spectrum of a toluene solution of2mCzBPDBq, and FIG. 35B shows an emission spectrum thereof. FIG. 36Ashows an absorption spectrum of a thin film of 2mCzBPDBq, and FIG. 36Bshows an emission spectrum thereof. The absorption spectrum was measuredusing an ultraviolet-visible spectrophotometer (V-550, produced by JASCOCorporation). The measurements were performed with samples prepared insuch a manner that the solution was put in a quartz cell and the thinfilm was obtained by evaporation onto a quartz substrate. The absorptionspectrum of the solution was obtained by subtracting the absorptionspectra of quartz and toluene from those of quartz and the solution, andthe absorption spectrum of the thin film was obtained by subtracting theabsorption spectrum of a quartz substrate from those of the quartzsubstrate and the thin film. In FIGS. 35A and 35B and FIGS. 36A and 36B,the horizontal axis represents wavelength (nm) and the vertical axisrepresents intensity (arbitrary unit). In the case of the toluenesolution, absorption peaks were observed at around 341 nm, 362 nm, and374 nm, and emission wavelength peaks were 386 nm and 403 nm (at anexcitation wavelength of 374 nm). In the case of the thin film,absorption peaks were observed at around 208 nm, 253 nm, 294 nm, 313 nm,328 nm, 345 nm, 369 nm, and 384 nm, and an emission wavelength peak was444 nm (at an excitation wavelength of 382 nm).

Example 10 Synthesis Example 9

This example gives descriptions of a method of synthesizing2-[3-(3,6-diphenyl-9H-carbazol-9-yl)phenyl]dibenzo[f,h]quinoxaline(abbreviation: 2mCzPDBq-III) represented by the following StructuralFormula (326).

[Synthesis of 2mCzPDBq-III]

A scheme for the synthesis of 2mCzPDBq-III is illustrated in (C-9).

In a 100-mL three-neck flask were put 0.54 g (2.0 mmol) of2-chlorodibenzo[f,h]quinoxaline, 0.94 g (2.1 mmol) of3-(3,6-diphenyl-9H-carbazol-9-yl)phenylboronic acid, 20 mL of toluene,2.0 mL of ethanol, and 2.0 mL of a 2M aqueous potassium carbonatesolution. This mixture was degassed by stirring under reduced pressure,and the air in the flask was replaced with nitrogen. To this mixture wasadded 46 mg (39 μmol) of tetrakis(triphenylphosphine)palladium(0). Thismixture was stirred under a nitrogen stream at 80° C. for 11 hours.After a predetermined time had elapsed, water was added to the obtainedmixture, and organic substances were extracted from the aqueous layerwith toluene. The obtained solution of the extracted organic substanceswas combined with the organic layer, the mixture was washed withsaturated brine, and the organic layer was dried with magnesium sulfate.The obtained mixture was gravity filtered, and the filtrate wasconcentrated to give a solid. The obtained solid was dissolved intoluene, and the toluene solution was suction filtered through alumina,Florisil (produced by Wako Pure Chemical Industries, Ltd., Catalog No.540-00135), and Celite (produced by Wako Pure Chemical Industries, Ltd.,Catalog No. 531-16855), and the obtained filtrate was concentrated togive a solid. The obtained solid was purified by silica gel columnchromatography (with a developing solvent of toluene and hexane in aratio of 2:1). Further, recrystallization from toluene gave 0.90 g of ayellow powder in 70% yield, which was the substance to be produced.

By a train sublimation method, 0.89 g of the obtained yellow powder waspurified. In the purification, the yellow powder was heated at 310° C.under a pressure of 3.0 Pa with a flow rate of argon gas of 5 mL/min.After the purification, 0.80 g of a yellow powder was obtained in ayield of 89%, which was the substance to be produced.

A nuclear magnetic resonance (NMR) method identified this compound as2-[3-(3,6-diphenyl-9H-carbazol-9-yl)phenyl]dibenzo[f,h]quinoxaline(abbreviation: 2mCzPDBq-III), which was the substance to be produced.

¹H NMR data of the obtained substance are as follows: ¹H NMR (CDCl₃, 300MHz): δ=7.37 (t, J=7.2 Hz, 2H), 7.50 (t, J=7.2 Hz, 4H), 7.63 (d, J=8.4Hz, 2H), 7.71-7.84 (m, 11H), 7.88 (t, J=7.8 Hz, 1H), 8.43-8.46 (m, 3H),8.64-8.68 (m, 3H), 9.25 (dd, J=7.8 Hz, 1.8 Hz, 1H), 9.36 (dd, J=7.8 Hz,1.5 Hz, 1H), 9.47 (s, 1H).

FIGS. 37A and 37B illustrate the ¹H NMR charts. Note that FIG. 37B is achart showing an enlarged part of FIG. 37A in the range of 7.0 ppm to10.0 ppm.

Further, FIG. 38A shows an absorption spectrum of a toluene solution of2mCzPDBq-III, and FIG. 38B shows an emission spectrum thereof. FIG. 39Ashows an absorption spectrum of a thin film of 2mCzPDBq-III, and FIG.39B shows an emission spectrum thereof. The absorption spectrum wasmeasured using an ultraviolet-visible spectrophotometer (V-550, producedby JASCO Corporation). The measurements were performed with samplesprepared in such a manner that the solution was put in a quartz cell andthe thin film was obtained by evaporation onto a quartz substrate. Theabsorption spectrum of the solution was obtained by subtracting theabsorption spectra of quartz and toluene from those of quartz and thesolution, and the absorption spectrum of the thin film was obtained bysubtracting the absorption spectrum of a quartz substrate from those ofthe quartz substrate and the thin film. In FIGS. 38A and 38B and FIGS.39A and 39B, the horizontal axis represents wavelength (nm) and thevertical axis represents intensity (arbitrary unit). In the case of thetoluene solution, absorption peaks were observed at around 299 nm, 360nm, and 374 nm, and an emission wavelength peak was 443 nm (at anexcitation wavelength of 375 nm). In the case of the thin film,absorption peaks were observed at around 264 nm, 304 nm, 367 nm, and 380nm, and an emission wavelength peak was 462 nm (at an excitationwavelength of 381 nm).

Example 11 Synthesis Example 10

This example gives descriptions of a method of synthesizing2-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]dibenzo[f,h]quinoxaline(abbreviation: PCPDBq) represented by the following Structural Formula(400).

[Synthesis of PCPDBq]

A scheme for the synthesis of PCPDBq is illustrated in (C-10).

In a 200-mL three-neck flask were put 1.2 g (4.0 mmol) of2-chlorodibenzo[f,h]quinoxaline, 1.6 g (4.4 mmol) of4-(9-phenyl-9H-carbazol-3-yl)phenylboronic acid, 11 mg (0.05 mmol) ofpalladium(II) acetate, 30 mg (0.1 mmol) oftris(2-methylphenyl)phosphine, 30 mL of toluene, 3 mL of ethanol, and 3mL of a 2M aqueous potassium carbonate solution. The mixture wasdegassed by stirring under reduced pressure. Then, the mixture washeated and stirred under a nitrogen atmosphere at 85° C. for 40 hours.

After a predetermined time had elapsed, this mixed liquid was filteredand washed with water and toluene in this order. The substance obtainedby the filtration was purified by silica gel column chromatography. Atthis time, toluene was used as a developing solvent for thechromatography. The obtained fractions were concentrated, and methanolwas added thereto, followed by irradiation with ultrasonic waves. Theprecipitated solid was collected by suction filtration to give 1.2 g ofa yellow powder in 55% yield, which was the substance to be produced.

The Rf values of the produced substance and2-chlorodibenzo[f,h]quinoxaline were respectively 0.28 and 0.38, whichwere found by silica gel thin layer chromatography (TLC) (with adeveloping solvent of ethyl acetate and hexane in a ratio of 1:10).

A nuclear magnetic resonance (NMR) method identified this compound as2-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]dibenzo[f,h]quinoxaline(abbreviation: PCPDBq), which was the substance to be produced.

¹H NMR data of the obtained substance are as follows: ¹H NMR (CDCl₃, 300MHz): δ=7.32-7.37 (m, 1H), 7.43-7.53 (m, 4H), 7.59-7.68 (m, 4H),7.74-7.86 (m, 5H), 7.97 (d, J=8.1 Hz, 2H), 8.25 (d, J=7.2 Hz, 1H),8.47-8.50 (m, 3H), 8.66 (d, J=7.8 Hz, 2H), 9.23-9.27 (m, 1H), 9.45-9.49(m, 2H).

FIGS. 40A and 40B illustrate the ¹H NMR charts. Note that FIG. 40B is achart showing an enlarged part of FIG. 40A in the range of 7.0 ppm to10.0 ppm.

Further, FIG. 41A shows an absorption spectrum of a toluene solution ofPCPDBq, and FIG. 41B shows an emission spectrum thereof. FIG. 42A showsan absorption spectrum of a thin film of PCPDBq, and FIG. 42B shows anemission spectrum thereof. The absorption spectrum was measured using anultraviolet-visible spectrophotometer (V-550, produced by JASCOCorporation). The measurements were performed with samples prepared insuch a manner that the solution was put in a quartz cell and the thinfilm was obtained by evaporation onto a quartz substrate. The absorptionspectrum of the solution was obtained by subtracting the absorptionspectra of quartz and toluene from those of quartz and the solution, andthe absorption spectrum of the thin film was obtained by subtracting theabsorption spectrum of a quartz substrate from those of the quartzsubstrate and the thin film. In FIGS. 41A and 41B and FIGS. 42A and 42B,the horizontal axis represents wavelength (nm) and the vertical axisrepresents intensity (arbitrary unit). In the case of the toluenesolution, absorption peaks were observed at around 306 nm, 343 nm, and385 nm, and an emission wavelength peak was 428 nm (at an excitationwavelength of 385 nm). In the case of the thin film, absorption peakswere observed at around 251 nm, 262 nm, 285 nm, 315 nm, 353 nm, and 392nm, and an emission wavelength peak was 490 nm (at an excitationwavelength of 397 nm).

Example 12 Synthesis Example 11

This example gives descriptions of a method of synthesizing2-[3-(dibenzothiophen-2-yl)phenyl]dibenzo[f,h]quinoxaline (abbreviation:2mDBTPDBq) represented by the following Structural Formula (515).

[Synthesis of 2mDBTPDBq]

A scheme for the synthesis of 2mDBTPDBq is illustrated in (C-11).

In a 100-mL three-neck flask were put 0.32 g (1.0 mmol) of2-chlorodibenzo[f,h]quinoxaline, 0.32 g (1.1 mmol) of3-(dibenzothiophen-2-yl)phenylboronic acid, 10 mL of toluene, 1 mL ofethanol, and 2.0 mL of a 2M aqueous potassium carbonate solution. Thismixture was degassed by stirring under reduced pressure, and the air inthe flask was replaced with nitrogen. To this mixture was added 30 mg(20 μmol) of tetrakis(triphenylphosphine)palladium(0). This mixture wasstirred under a nitrogen stream at 80° C. for 8 hours. After apredetermined time had elapsed, water and toluene were added to thismixture, and organic substances were extracted from the aqueous layerwith toluene. The solution of the extracted organic substances wascombined with the organic layer, the mixture was washed with a saturatedaqueous solution of sodium hydrogen carbonate and saturated brine,followed by drying with magnesium sulfate. The obtained mixture wasgravity filtered, and then the filtrate was concentrated to give asolid. The obtained solid was dissolved in toluene, and the toluenesolution was suction filtered through alumina and Celite, and theobtained filtrate was concentrated to give a solid. The obtained solidwas recrystallized from toluene to give 0.13 g of a white powder in ayield of 26%, which was the substance to be produced.

A nuclear magnetic resonance (NMR) method identified this compound as2-[3-(dibenzothiophen-2-yl)phenyl]dibenzo[f,h]quinoxaline (abbreviation:2mDBTPDBq), which was the substance to be produced.

¹H NMR data of the obtained substance are as follows: ¹H NMR (CDCl₃, 300MHz): δ=7.50-7.53 (m, 2H), 7.72-7.93 (m, 8H), 8.02 (d, J=8.4 Hz, 1H),8.28-8.31 (m, 1H), 8.36 (d, J=7.5 Hz, 1H), 8.50 (d, J=1.5 Hz, 1H),8.67-8.70 (m, 3H), 9.27 (dd, J=7.8 Hz, 1.8 Hz, 1H), 9.46 (dd, J=7.8 Hz,1.8 Hz, 1H), 9.51 (s, 1H).

FIGS. 43A and 43B illustrate the ¹H NMR charts. Note that FIG. 43B is achart showing an enlarged part of FIG. 43A in the range of 7.0 ppm to10.0 ppm.

Further, FIG. 44A shows an absorption spectrum of a toluene solution of2mDBTPDBq, and FIG. 44B shows an emission spectrum thereof. FIG. 45Ashows an absorption spectrum of a thin film of 2mDBTPDBq, and FIG. 45Bshows an emission spectrum thereof. The absorption spectrum was measuredusing an ultraviolet-visible spectrophotometer (V-550, produced by JASCOCorporation). The measurements were performed with samples prepared insuch a manner that the solution was put in a quartz cell and the thinfilm was obtained by evaporation onto a quartz substrate. The absorptionspectrum of the solution was obtained by subtracting the absorptionspectra of quartz and toluene from those of quartz and the solution, andthe absorption spectrum of the thin film was obtained by subtracting theabsorption spectrum of a quartz substrate from those of the quartzsubstrate and the thin film. In FIGS. 44A and 44B and FIGS. 45A and 45B,the horizontal axis represents wavelength (nm) and the vertical axisrepresents intensity (arbitrary unit). In the case of the toluenesolution, absorption peaks were observed at around 362 nm and 374 nm,and emission wavelength peaks were 386 nm and 406 nm (at an excitationwavelength of 374 nm). In the case of the thin film, absorption peakswere observed at around 204 nm, 262 nm, 295 nm, 313 nm, 370 nm, and 384nm, and emission wavelength peaks were 443 nm and 571 nm (at anexcitation wavelength of 384 nm).

Example 13

In this example, a light-emitting element of one embodiment of thepresent invention will be described referring to FIG. 18. Chemicalformulae of materials used in this example are illustrated below. Notethat the chemical formulae of the materials which are illustrated aboveare omitted.

A method of fabricating Light-emitting Element 5 of this example will bedescribed below.

(Light-Emitting Element 5)

First, ITSO was deposited over the glass substrate 1100 by a sputteringmethod, whereby the first electrode 1101 was formed. Note that itsthickness was set to 110 nm and the electrode area was set to 2 mm×2 mm.Here, the first electrode 1101 is an electrode that functions as ananode of the light-emitting element.

Next, as pretreatment for forming the light-emitting element over thesubstrate 1100, after washing of a surface of the substrate with waterand baking that was performed at 200° C. for one hour, UV ozonetreatment was performed for 370 seconds.

After that, the substrate was transferred into a vacuum evaporationapparatus where the pressure had been reduced to approximately 10⁻⁴ Pa,and subjected to vacuum baking at 170° C. for 30 minutes in a heatingchamber of the vacuum evaporation apparatus, and then the substrate 1100was cooled down for about 30 minutes.

Next, the substrate 1100 provided with the first electrode 1101 wasfixed to a substrate holder in a vacuum evaporation apparatus so that asurface on which the first electrode 1101 was provided faced downward.The pressure in the vacuum evaporation apparatus was reduced to about10⁻⁴ Pa. Then, by an evaporation method using resistance heating, BPAFLPand molybdenum(VI) oxide were co-evaporated to form the hole-injectionlayer 1111 over the first electrode 1101. The thickness of thehole-injection layer 1111 was set to 40 nm, and the weight ratio ofBPAFLP to molybdenum(VI) oxide was adjusted to 4:2(=BPAFLP:molybdenum(VI) oxide). Note that the co-evaporation methodrefers to an evaporation method in which evaporation is carried out froma plurality of evaporation sources at the same time in one treatmentchamber.

Next, a BPAFLP film was formed to a thickness of 20 nm over thehole-injection layer 1111, whereby the hole-transport layer 1112 wasformed.

Further, 2-[4-(dibenzothiophen-4-yl)phenyl]dibenzo quinoxaline(abbreviation: 2DBTPDBq-II) synthesized in Example4,4,4′-di(1-naphthyl)-4″-(9-phenyl-9H-carbazol-3-yl)triphenylamine(abbreviation: PCBNBB), and(dipivaloylmethanato)bis(3,5-dimethyl-2-phenylpyrazinato)iridium(III)(abbreviation: [Ir(mppr-Me)₂(dpm)]) were co-evaporated to form thelight-emitting layer 1113 over the hole-transport layer 1112. The weightratio of 2DBTPDBq-II to PCBNBB and [Ir(mppr-Me)₂(dpm)] was adjusted to0.8:0.2:0.05 (=2DBTPDBq-II:PCBNBB:[Ir(mppr-Me)₂(dpm)]). The thickness ofthe light-emitting layer 1113 was set to 40 nm.

Further, a 2DBTPDBq-II film was formed to a thickness of 10 nm over thelight-emitting layer 1113, whereby the first electron-transport layer1114 a was formed.

Then, a BPhen film was formed to a thickness of 20 nm over the firstelectron-transport layer 1114 a, whereby the second electron-transportlayer 1114 b was formed.

Further, a LiF film was formed to a thickness of 1 nm over the secondelectron-transport layer 1114 b by evaporation, whereby theelectron-injection layer 1115 was formed.

Lastly, an aluminum film was formed to a thickness of 200 nm byevaporation as the second electrode 1103 functioning as a cathode. Thus,Light-emitting Element 5 of this example was fabricated.

Note that, in the above evaporation process, evaporation was allperformed by a resistance heating method.

Table 3 shows an element structure of Light-emitting Element 5 obtainedas described above.

TABLE 3 First Second Hole- Hole- Light- electron- electron- Electron-First injection transport emitting transport transport injection Secondelectrode layer layer layer layer layer layer electrode Light- ITSOBPAFLP: BPAFLP 2DBTPDBq- II: 2DBTPDBq-II BPhen LiF Al emitting 110 nmMoOx 20 nm PCBNBB: 10 nm 20 nm 1 nm 200 nm element 5 (=4:2)[Ir(mppr-Me)₂(dpm)] 40 nm (=0.8:0.2:0.05) 40 nm

In a glove box containing a nitrogen atmosphere, Light-emitting Element5 was sealed with a glass substrate so as not to be exposed to air.Then, operation characteristics of the element were measured. Note thatthe measurements were carried out at room temperature (in the atmospherekept at 25° C.).

FIG. 46 shows the voltage vs. luminance characteristics ofLight-emitting Element 5. In FIG. 46, the horizontal axis representsvoltage (V) and the vertical axis represents luminance (cd/m²). Inaddition, FIG. 47 shows the luminance vs. current efficiencycharacteristics of the element. In FIG. 47, the horizontal axisrepresents luminance (cd/m²) and the vertical axis represents currentefficiency (cd/A). Further, Table 4 shows the voltage (V), currentdensity (mA/cm²), CIE chromaticity coordinates (x, y), currentefficiency (cd/A), and external quantum efficiency (%) of thelight-emitting element at a luminance of 1100 cd/m².

TABLE 4 External Current Chroma- Chroma- Current quantum Voltage densityticity ticity Luminance efficiency efficiency (V) (mA/cm²) x y (cd/m²)(cd/A) (%) Light- 2.8 1.6 0.55 0.45 1100 67 25 emitting element 5

As shown in Table 4, the CIE chromaticity coordinates (x, y) ofLight-emitting Element 5 were (0.55, 0.45) at a luminance of 1100 cd/m².It is found that Light-emitting Element 5 exhibited light emission from[Ir(mppr-Me)₂(dpm)].

FIG. 46 and FIG. 47 reveal that Light-emitting Element 5 has low drivingvoltage and high current efficiency. It is thus confirmed that acompound to which one embodiment of the present invention is applied iseffective in realizing high voltage vs. luminance characteristics andhigh luminance vs. current efficiency characteristics.

As described above, by using 2DBTPDBq-II produced in Example 4 as a hostmaterial of a light-emitting layer, a light-emitting element having lowdriving voltage and high current efficiency was able to be fabricated.

Next, Light-emitting Element 5 was subjected to reliability tests.Results of the reliability tests are shown in FIG. 48. In FIG. 48, thevertical axis represents normalized luminance (%) with an initialluminance of 100%, and the horizontal axis represents driving time (h)of the element. In the reliability tests, the light-emitting element ofthis example was driven under the conditions where the current densitywas constant and the initial luminance was 5000 cd/m². FIG. 48 showsthat Light-emitting Element 5 kept 82% of the initial luminance afterdriving for 430 hours. These results of the reliability tests revealedthat Light-emitting Element 5 had a long lifetime.

As described above, by the use of 2DBTPDBq-II produced in Example 4 as ahost material of a light-emitting layer, a light-emitting element havinga long lifetime was able to be fabricated.

Example 14

In this example, a light-emitting element of one embodiment of thepresent invention will be described referring to FIG. 18. Chemicalformulae of materials used in this example are illustrated below. Notethat the chemical formulae of the materials which are illustrated aboveare omitted.

A method of fabricating Light-emitting Element 6 of this example will bedescribed below.

(Light-Emitting Element 6)

First, the first electrode 1101, the hole-injection layer 1111, and thehole-transport layer 1112 were formed over the glass substrate 1100 inthe same manner as those of Light-emitting Element 5 described inExample 13.

Next, 2-[3′-(dibenzothiophen-4-yl)biphenyl-3-yl]dibenzo[f,h]quinoxaline(abbreviation: 2mDBTBPDBq-II) synthesized in Example 5, PCBNBB, and[Ir(mppr-Me)₂(dpm)]) were co-evaporated to form the light-emitting layer1113 over the hole-transport layer 1112. The weight ratio of2mDBTBPDBq-II to PCBNBB and [Ir(mppr-Me)₂(dpm)] was adjusted to0.8:0.2:0.05 (=2mDBTBPDBq-II:PCBNBB:[Ir(mppr-Me)₂(dpm)]). The thicknessof the light-emitting layer 1113 was set to 40 nm.

Further, a 2mDBTBPDBq-II film was formed to a thickness of 10 nm overthe light-emitting layer 1113, whereby the first electron-transportlayer 1114 a was formed.

Then, a BPhen film was formed to a thickness of 20 nm over the firstelectron-transport layer 1114 a, whereby the second electron-transportlayer 1114 b was formed.

Further, a LiF film was formed to a thickness of 1 nm over the secondelectron-transport layer 1114 b by evaporation, whereby theelectron-injection layer 1115 was formed.

Lastly, an aluminum film was formed to a thickness of 200 nm byevaporation as the second electrode 1103 functioning as a cathode. Thus,Light-emitting Element 6 of this example was fabricated.

Note that, in the above evaporation process, evaporation was allperformed by a resistance heating method.

Table 5 shows an element structure of Light-emitting Element 6 obtainedas described above.

TABLE 5 First Second Hole- Hole- Light- electron- electron- Electron-First injection transport emitting transport transport injection Secondelectrode layer layer layer layer layer layer electrode Light- ITSOBPAFLP: BPAFLP 2mDBTBPDBq- II: 2mDBTBPDBq-II BPhen LiF Al emitting 110nm MoOx 20 nm PCBNBB: 10 nm 20 nm 1 nm 200 nm element 6 (=4:2)[Ir(mppr-Me)₂(dpm)] 40 nm (=0.8:0.2:0.05) 40 nm

In a glove box containing a nitrogen atmosphere, Light-emitting Element6 was sealed with a glass substrate so as not to be exposed to air.Then, operation characteristics of the element were measured. Note thatthe measurements were carried out at room temperature (in the atmospherekept at 25° C.).

FIG. 49 shows the voltage vs. luminance characteristics ofLight-emitting Element 6. In FIG. 49, the horizontal axis representsvoltage (V) and the vertical axis represents luminance (cd/m²). Inaddition, FIG. 50 shows the luminance vs. current efficiencycharacteristics of the element. In FIG. 50, the horizontal axisrepresents luminance (cd/m²) and the vertical axis represents currentefficiency (cd/A). Further, Table 6 shows the voltage (V), currentdensity (mA/cm²), CIE chromaticity coordinates (x, y), currentefficiency (cd/A), and external quantum efficiency (%) of thelight-emitting element at a luminance of 1000 cd/m².

TABLE 6 External Current Chroma- Chroma- Current quantum Voltage densityticity ticity Luminance efficiency efficiency (V) (mA/cm²) x y (cd/m²)(cd/A) (%) Light- 2.9 1.4 0.53 0.47 1000 71 25 emitting element 6

As shown in Table 6, the CIE chromaticity coordinates (x, y) ofLight-emitting Element 6 were (0.53, 0.47) at a luminance of 1000 cd/m².It is found that Light-emitting Element 6 exhibited light emission from[Ir(mppr-Me)₂(dpm)].

FIG. 49 and FIG. 50 reveal that Light-emitting Element 6 has low drivingvoltage and high current efficiency. It is thus confirmed that acompound to which one embodiment of the present invention is applied iseffective in realizing high voltage vs. luminance characteristics andhigh luminance vs. current efficiency characteristics.

As described above, by using 2mDBTBPDBq-II produced in Example 5 as ahost material of a light-emitting layer, a light-emitting element havinglow driving voltage and high current efficiency was able to befabricated.

Next, Light-emitting Element 6 was subjected to reliability tests.Results of the reliability tests are shown in FIG. 51. In FIG. 51, thevertical axis represents normalized luminance (%) with an initialluminance of 100%, and the horizontal axis represents driving time (h)of the element. In the reliability tests, the light-emitting element ofthis example was driven under the conditions where the current densitywas constant and the initial luminance was 5000 cd/m². FIG. 51 showsthat Light-emitting Element 6 kept 82% of the initial luminance afterdriving for 710 hours. These results of the reliability tests revealedthat Light-emitting Element 6 had a long lifetime.

As described above, by using 2mDBTBPDBq-II produced in Example 5 as ahost material of a light-emitting layer, a light-emitting element havinga long lifetime was able to be fabricated. Further, particularly when anarylene group in a compound included in a light-emitting element,through which a dibenzo[f,h]quinoxaline ring and a hole-transportskeleton are bonded, is a biphenyldiyl group, it is found possible toextend the lifetime of the light-emitting element.

Example 15

In this example, a light-emitting element of one embodiment of thepresent invention will be described referring to FIG. 18. Chemicalformulae of materials used in this example are illustrated below. Notethat the chemical formulae of the materials which are illustrated aboveare omitted.

A method of fabricating Light-emitting Element 7 of this example will bedescribed below.

(Light-Emitting Element 7)

First, the first electrode 1101, the hole-injection layer 1111, and thehole-transport layer 1112 were formed over the glass substrate 1100 inthe same manner as those of Light-emitting Element 5 described inExample 13.

Next,2-[3-(2,8-diphenyldibenzothiophen-4-yl)phenyl]dibenzo[f,h]quinoxaline(abbreviation: 2mDBTPDBq-III) synthesized in Example 6, PCBNBB, and[Ir(mppr-Me)₂(dpm)]) were co-evaporated to form the light-emitting layer1113 over the hole-transport layer 1112. The weight ratio of2mDBTPDBq-III to PCBNBB and [Ir(mppr-Me)₂(dpm)] was adjusted to0.8:0.2:0.05 (=2mDBTPDBq-III:PCBNBB:[Ir(mppr-Me)₂(dpm)]). The thicknessof the light-emitting layer 1113 was set to 40 nm.

Further, a 2mDBTPDBq-III film was formed to a thickness of 10 nm overthe light-emitting layer 1113, whereby the first electron-transportlayer 1114 a was formed.

Then, a BPhen film was formed to a thickness of 20 nm over the firstelectron-transport layer 1114 a, whereby the second electron-transportlayer 1114 b was formed.

Further, a LiF film was formed to a thickness of 1 nm over the secondelectron-transport layer 1114 b by evaporation, whereby theelectron-injection layer 1115 was formed.

Lastly, an aluminum film was for lied to a thickness of 200 nm byevaporation as the second electrode 1103 functioning as a cathode. Thus,Light-emitting Element 7 of this example was fabricated.

Note that, in the above evaporation process, evaporation was allperformed by a resistance heating method.

Table 7 shows an element structure of Light-emitting Element 7 obtainedas described above.

TABLE 7 First Second Hole- Hole- Light- electron- electron- Electron-First injection transport emitting transport transport injection Secondelectrode layer layer layer layer layer layer electrode Light- ITSOBPAFLP: BPAFLP 2mDBTPDBq-III: 2mDBTPDBq-III BPhen LiF Al emitting 110 nmMoOx 20 nm PCBNBB: 10 nm 20 nm 1 nm 200 nm element 7 (=4:2)[Ir(mppr-Me)₂(dpm)] 40 nm (=0.8:0.2:0.05) 40 nm

In a glove box containing a nitrogen atmosphere, Light-emitting Element7 was sealed with a glass substrate so as not to be exposed to air.Then, operation characteristics of the element were measured. Note thatthe measurements were carried out at room temperature (in the atmospherekept at 25° C.).

FIG. 52 shows the voltage vs. luminance characteristics ofLight-emitting Element 7. In FIG. 52, the horizontal axis representsvoltage (V) and the vertical axis represents luminance (cd/m²). Inaddition, FIG. 53 shows the luminance vs. current efficiencycharacteristics of the element. In FIG. 53, the horizontal axisrepresents luminance (cd/m²) and the vertical axis represents currentefficiency (cd/A). Further, Table 8 shows the voltage (V), currentdensity (mA/cm²), CIE chromaticity coordinates (x, y), currentefficiency (cd/A), and external quantum efficiency (%) of thelight-emitting element at a luminance of 910 cd/m².

TABLE 8 External Current Chroma- Chroma- Current quantum Voltage densityticity ticity Luminance efficiency efficiency (V) (mA/cm²) x y (cd/m²)(cd/A) (%) Light- 2.9 1.4 0.55 0.45 910 65 24 emitting element 7

As shown in Table 8, the CIE chromaticity coordinates (x, y) ofLight-emitting Element 7 were (0.55, 0.45) at a luminance of 910 cd/m².It is found that Light-emitting Element 7 exhibited light emission from[Ir(mppr-Me)₂(dpm)].

FIG. 52 and FIG. 53 reveal that Light-emitting Element 7 has low drivingvoltage and high current efficiency. It is thus continued that acompound to which one embodiment of the present invention is applied iseffective in realizing high voltage vs. luminance characteristics andhigh luminance vs. current efficiency characteristics.

As described above, by using 2mDBTPDBq-III produced in Example 6 as ahost material of a light-emitting layer, a light-emitting element havinglow driving voltage and high current efficiency was able to befabricated.

Example 16

In this example, a light-emitting element of one embodiment of thepresent invention will be described referring to FIG. 18. Chemicalformulae of materials used in this example are illustrated below. Notethat the chemical formulae of the materials which are illustrated aboveare omitted.

A method of fabricating Light-emitting Element 8 of this example will bedescribed below.

(Light-Emitting Element 8)

First, the first electrode 1101, the hole-injection layer 1111, and thehole-transport layer 1112 were formed over the glass substrate 1100 inthe same manner as those of Light-emitting Element 5 described inExample 13.

Next, 2-[3-(dibenzothiophen-4-yl)phenyl]-3-phenyldibenzo[f,h]quinoxaline(abbreviation: 3Ph-2mDBTPDBq-II) synthesized in Example 7, PCBA1BP, and[Ir(mppr-Me)₂(acac)]) were co-evaporated to form the light-emittinglayer 1113 over the hole-transport layer 1112. The weight ratio of3Ph-2mDBTPDBq-II to PCBA1BP and [Ir(mppr-Me)₂(acac)] was adjusted to1:0.15:0.06 (=3Ph-2mDBTPDBq-II:PCBA1BP:[Ir(mppr-Me)₂(acac)]). Thethickness of the light-emitting layer 1113 was set to 40 nm.

Further, a 3Ph-2mDBTPDBq-II film was formed to a thickness of 10 nm overthe light-emitting layer 1113, whereby the first electron-transportlayer 1114 a was formed.

Then, a BPhen film was formed to a thickness of 20 nm over the firstelectron-transport layer 1114 a, whereby the second electron-transportlayer 1114 b was formed.

Further, a LiF film was formed to a thickness of 1 nm over the secondelectron-transport layer 1114 b by evaporation, whereby theelectron-injection layer 1115 was formed.

Lastly, an aluminum film was formed to a thickness of 200 nm byevaporation as the second electrode 1103 functioning as a cathode. Thus,Light-emitting Element 8 of this example was fabricated.

Note that, in the above evaporation process, evaporation was allperformed by a resistance heating method.

Table 9 shows an element structure of Light-emitting Element 8 obtainedas described above.

TABLE 9 First Second Hole- Hole- Light- electron- electron- Electron-First injection transport emitting transport transport injection Secondelectrode layer layer layer layer layer layer electrode Light- ITSOBPAFLP: BPAFLP 3Ph-2mDBTPDBq- II: 3Ph-2mDBTPDBq-II BPhen LiF Al emitting110 nm MoOx 20 nm PCBA1BP: 10 nm 20 nm 1 nm 200 nm element 8 (=4:2)[Ir(mppr-Me)₂(acac)] 40 nm (=1:0.15:0.06) 40 nm

In a glove box containing a nitrogen atmosphere, Light-emitting Element8 was sealed with a glass substrate so as not to be exposed to air.Then, operation characteristics of the element were measured. Note thatthe measurements were carried out at room temperature (in the atmospherekept at 25° C.).

FIG. 54 shows the voltage vs. luminance characteristics ofLight-emitting Element 8. In FIG. 54, the horizontal axis representsvoltage (V) and the vertical axis represents luminance (cd/m²). Inaddition, FIG. 55 shows the luminance vs. current efficiencycharacteristics of the element. In FIG. 55, the horizontal axisrepresents luminance (cd/m²) and the vertical axis represents currentefficiency (cd/A). Further, Table 10 shows the voltage (V), currentdensity (mA/cm²), CIE chromaticity coordinates (x, y), currentefficiency (cd/A), and external quantum efficiency (%) of thelight-emitting element at a luminance of 810 cd/m².

TABLE 10 External Current Chroma- Chroma- Current quantum Voltagedensity ticity ticity Luminance efficiency efficiency (V) (mA/cm²) x y(cd/m²) (cd/A) (%) Light- 3.0 1.6 0.55 0.45 810 52 20 emitting element 8

As shown in Table 10, the CIE chromaticity coordinates (x, y) ofLight-emitting Element 8 were (0.55, 0.45) at a luminance of 810 cd/m².It is found that Light-emitting Element 8 exhibited light emission from[Ir(mppr-Me)₂(acac)].

FIG. 54 and FIG. 55 reveal that Light-emitting Element 8 has low drivingvoltage and high current efficiency. It is thus confirmed that acompound to which one embodiment of the present invention is applied iseffective in realizing high voltage vs. luminance characteristics andhigh luminance vs. current efficiency characteristics.

As described above, by using 3Ph-2mDBTPDBq-II produced in Example 7 as ahost material of a light-emitting layer, a light-emitting element havinglow driving voltage and high current efficiency was able to befabricated.

Example 17

In this example, a light-emitting element of one embodiment of thepresent invention will be described referring to FIG. 18. Chemicalformulae of materials used in this example are illustrated below. Notethat the chemical formulae of the materials which are illustrated aboveare omitted.

A method of fabricating Light-emitting Element 9 of this example will bedescribed below.

(Light-Emitting Element 9)

First, the first electrode 1101, the hole-injection layer 1111, and thehole-transport layer 1112 were formed over the glass substrate 1100 inthe same manner as those of Light-emitting Element 5 described inExample 13.

Next, 2-[3-(dibenzofuran-4-yl)phenyl]dibenzo[f,h]quinoxaline(abbreviation: 2mDBFPDBq-II) synthesized in Example 8, PCBNBB, and[Ir(mppr-Me)₂(dpm)]) were co-evaporated to form the light-emitting layer1113 over the hole-transport layer 1112. The weight ratio of2mDBFPDBq-II to PCBNBB and [Ir(mppr-Me)₂(dpm)] was adjusted to0.8:0.2:0.05 (=2mDBFPDBq-II:PCBNBB: [Ir(mppr-Me)₂(dpm)]). The thicknessof the light-emitting layer 1113 was set to 40 nm.

Further, a 2mDBFPDBq-II film was formed to a thickness of 10 nm over thelight-emitting layer 1113, whereby the first electron-transport layer1114 a was formed.

Then, a bathophenanthroline (abbreviation: BPhen) film was formed to athickness of 20 nm over the first electron-transport layer 1114 a,whereby the second electron-transport layer 1114 b was formed.

Further, a lithium fluoride (LiF) film was formed to a thickness of 1 nmover the second electron-transport layer 1114 b by evaporation, wherebythe electron-injection layer 1115 was formed.

Lastly, an aluminum film was formed to a thickness of 200 nm byevaporation as the second electrode 1103 functioning as a cathode. Thus,Light-emitting Element 9 of this example was fabricated.

Note that, in the above evaporation process, evaporation was allperformed by a resistance heating method.

Table 11 shows an element structure of Light-emitting Element 9 obtainedas described above.

TABLE 11 First Second Hole- Hole- Light- electron- electron- Electron-First injection transport emitting transport transport injection Secondelectrode layer layer layer layer layer layer electrode Light- ITSOBPAFLP: BPAFLP 2mDBFPDBq- II: 2mDBFPDBq-II BPhen LiF Al emitting 110 nmMoOx 20 nm PCBNBB: 10 nm 20 nm 1 nm 200 nm element 9 (=4:2)[Ir(mppr-Me)₂(dpm)] 40 nm (=0.8:0.2:0.05) 40 nm

In a glove box containing a nitrogen atmosphere, Light-emitting Element9 was sealed with a glass substrate so as not to be exposed to air.Then, operation characteristics of the element were measured. Note thatthe measurements were carried out at room temperature (in the atmospherekept at 25° C.).

FIG. 56 shows the voltage vs. luminance characteristics ofLight-emitting Element 9. In FIG. 56, the horizontal axis representsvoltage (V) and the vertical axis represents luminance (cd/m²). Inaddition, FIG. 57 shows the luminance vs. current efficiencycharacteristics of the element. In FIG. 57, the horizontal axisrepresents luminance (cd/m²) and the vertical axis represents currentefficiency (cd/A). Further, Table 12 shows the voltage (V), currentdensity (mA/cm²), CIE chromaticity coordinates (x, y), currentefficiency (cd/A), and external quantum efficiency (%) of thelight-emitting element at a luminance of 990 cd/m².

TABLE 12 External Current Chroma- Chroma- Current quantum Voltagedensity ticity ticity Luminance efficiency efficiency (V) (mA/cm²) x y(cd/m²) (cd/A) (%) Light- 3.0 1.5 0.55 0.45 990 64 24 emitting element 9

As shown in Table 12, the CIE chromaticity coordinates (x, y) ofLight-emitting Element 9 were (0.55, 0.45) at a luminance of 990 cd/m².It is found that Light-emitting Element 9 exhibited light emission from[Ir(mppr-Me)₂(dpm)].

FIG. 56 and FIG. 57 reveal that Light-emitting Element 9 has low drivingvoltage and high current efficiency. It is thus confirmed that acompound to which one embodiment of the present invention is applied iseffective in realizing high voltage vs. luminance characteristics andhigh luminance vs. current efficiency characteristics.

As described above, by using 2mDBFPDBq-II produced in Example 8 as ahost material of a light-emitting layer, a light-emitting element havinglow driving voltage and high current efficiency was able to befabricated.

Example 18

In this example, a light-emitting element of one embodiment of thepresent invention will be described referring to FIG. 18. Chemicalformulae of materials used in this example are illustrated below. Notethat the chemical formulae of the materials which are illustrated aboveare omitted.

A method of fabricating Light-emitting Element 10 of this example willbe described below.

(Light-Emitting Element 10)

First, the first electrode 1101, the hole-injection layer 1111, and thehole-transport layer 1112 were formed over the glass substrate 1100 inthe same manner as those of Light-emitting Element 5 described inExample 13.

Next, 2-[3-(3,6-diphenyl-9H-carbazol-9-yl)phenyl]dibenzo[f,h]quinoxaline(abbreviation: 2mCzPDBq-III) synthesized in Example 10, PCBNBB, and[Ir(mppr-Me)₂(dpm)]) were co-evaporated to form the light-emitting layer1113 over the hole-transport layer 1112. The weight ratio of2mCzPDBq-III to PCBNBB and [Ir(mppr-Me)₂(dpm)] was adjusted to0.8:0.2:0.05 (=2mCzPDBq-III:PCBNBB: [Ir(mppr-Me)₂(dpm)]). The thicknessof the light-emitting layer 1113 was set to 40 nm.

Further, a 2mCzPDBq-III film was formed to a thickness of 10 nm over thelight-emitting layer 1113, whereby the first electron-transport layer1114 a was formed.

Then, a BPhen film was formed to a thickness of 20 nm over the firstelectron-transport layer 1114 a, whereby the second electron-transportlayer 1114 b was formed.

Further, a LiF film was formed to a thickness of 1 nm over the secondelectron-transport layer 1114 b by evaporation, whereby theelectron-injection layer 1115 was formed.

Lastly, an aluminum film was formed to a thickness of 200 nm byevaporation as the second electrode 1103 functioning as a cathode. Thus,Light-emitting Element 10 of this example was fabricated.

Note that, in the above evaporation process, evaporation was allperformed by a resistance heating method.

Table 13 shows an element structure of Light-emitting Element 10obtained as described above.

TABLE 13 First Second Hole- Hole- Light- electron- electron- Electron-First injection transport emitting transport transport injection Secondelectrode layer layer layer layer layer layer electrode Light- ITSOBPAFLP: BPAFLP 2mCzPDBq-III: 2mCzPDBq-III BPhen LiF Al emitting 110 nmMoOx 20 nm PCBNBB: 10 nm 20 nm 1 nm 200 nm element 10 (=4:2)[Ir(mppr-Me)₂(dpm)] 40 nm (=0.8:0.2:0.05) 40 nm

In a glove box containing a nitrogen atmosphere, Light-emitting Element10 was sealed with a glass substrate so as not to be exposed to air.Then, operation characteristics of the element were measured. Note thatthe measurements were carried out at room temperature (in the atmospherekept at 25° C.).

FIG. 58 shows the voltage vs. luminance characteristics ofLight-emitting Element 10. In FIG. 58, the horizontal axis representsvoltage (V) and the vertical axis represents luminance (cd/m²). Inaddition, FIG. 59 shows the luminance vs. current efficiencycharacteristics of the element. In FIG. 59, the horizontal axisrepresents luminance (cd/m²) and the vertical axis represents currentefficiency (cd/A). Further, Table 14 shows the voltage (V), currentdensity (mA/cm²), CIE chromaticity coordinates (x, y), currentefficiency (cd/A), and external quantum efficiency (%) of thelight-emitting element at a luminance of 870 cd/m².

TABLE 14 External Current Chroma- Chroma- Current quantum Voltagedensity ticity ticity Luminance efficiency efficiency (V) (mA/cm²) x y(cd/m²) (cd/A) (%) Light- 3.0 1.3 0.55 0.45 870 69 26 emitting element10

As shown in Table 14, the CIE chromaticity coordinates (x, y) ofLight-emitting Element 10 were (0.55, 0.45) at a luminance of 870 cd/m².It is found that Light-emitting Element 10 exhibited light emission from[Ir(mppr-Me)₂(dpm)].

FIG. 58 and FIG. 59 reveal that Light-emitting Element 10 has lowdriving voltage and high current efficiency. It is thus confirmed that acompound to which one embodiment of the present invention is applied iseffective in realizing high voltage vs. luminance characteristics andhigh luminance vs. current efficiency characteristics.

As described above, by using 2mCzPDBq-III produced in Example 10 as ahost material of a light-emitting layer, a light-emitting element havinglow driving voltage and high current efficiency was able to befabricated.

Example 19

In this example, a light-emitting element of one embodiment of thepresent invention will be described referring to FIG. 18. Chemicalformulae of materials used in this example are illustrated below. Notethat the chemical formulae of the materials which are illustrated aboveare omitted.

A method of fabricating Light-emitting Element 11 of this example willbe described below.

(Light-Emitting Element 11)

First, the first electrode 1101, the hole-injection layer 1111, and thehole-transport layer 1112 were formed over the glass substrate 1100 inthe same manner as those of Light-emitting Element 5 described inExample 13.

Next, 2-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]dibenzo[f,h]quinoxaline(abbreviation: PCPDBq) synthesized in Example 11, PCBNBB, and[Ir(mppr-Me)₂(dpm)]) were co-evaporated to form the light-emitting layer1113 over the hole-transport layer 1112. The weight ratio of PCPDBq toPCBNBB and [Ir(mppr-Me)₂(dpm)] was adjusted to 0.8:0.2:0.05(=PCPDBq:PCBNBB:[Ir(mppr-Me)₂(dpm)]). The thickness of thelight-emitting layer 1113 was set to 40 nm.

Further, a PCPDBq film was formed to a thickness of 10 nm over thelight-emitting layer 1113, whereby the first electron-transport layer1114 a was formed.

Then, a bathophenanthroline (abbreviation: BPhen) film was formed to athickness of 20 nm over the first electron-transport layer 1114 a,whereby the second electron-transport layer 1114 b was formed.

Further, a lithium fluoride (LiF) film was formed to a thickness of 1 nmover the second electron-transport layer 1114 b by evaporation, wherebythe electron-injection layer 1115 was formed.

Lastly, an aluminum film was formed to a thickness of 200 nm byevaporation as the second electrode 1103 functioning as a cathode. Thus,Light-emitting Element 11 of this example was fabricated.

Note that, in the above evaporation process, evaporation was allperformed by a resistance heating method.

Table 15 shows an element structure of Light-emitting Element 11obtained as described above.

TABLE 15 First Second Hole- Hole- Light- electron- electron- Electron-First injection transport emitting transport transport injection Secondelectrode layer layer layer layer layer layer electrode Light- ITSOBPAFLP: BPAFLP PCPDBq: PCPDBq BPhen LiF Al emitting 110 nm MoOx 20 nmPCBNBB: 10 nm 20 nm 1 nm 200 nm element 11 (=4:2) [Ir(mppr-Me)₂(dpm)] 40nm (=0.8:0.2:0.05) 40 nm

In a glove box containing a nitrogen atmosphere, Light-emitting Element11 was sealed with a glass substrate so as not to be exposed to air.Then, operation characteristics of the element were measured. Note thatthe measurements were carried out at room temperature (in the atmospherekept at 25° C.).

FIG. 60 shows the voltage vs. luminance characteristics ofLight-emitting Element 11. In FIG. 60, the horizontal axis representsvoltage (V) and the vertical axis represents luminance (cd/m²). Inaddition, FIG. 61 shows the luminance vs. current efficiencycharacteristics of the element. In FIG. 61, the horizontal axisrepresents luminance (cd/m²) and the vertical axis represents currentefficiency (cd/A). Further, Table 16 shows the voltage (V), currentdensity (mA/cm²), CIE chromaticity coordinates (x, y), currentefficiency (cd/A), and external quantum efficiency (%) of thelight-emitting element at a luminance of 860 cd/m².

TABLE 16 External Current Chroma- Chroma- Current quantum Voltagedensity ticity ticity Luminance efficiency efficiency (V) (mA/cm²) x y(cd/m²) (cd/A) (%) Light- 2.8 1.6 0.55 0.44 860 54 21 emitting element11

As shown in Table 16, the CIE chromaticity coordinates (x, y) ofLight-emitting Element 11 were (0.55, 0.44) at a luminance of 860 cd/m².It is found that Light-emitting Element 11 exhibited light emission from[Ir(mppr-Me)₂(dpm)].

FIG. 60 and FIG. 61 reveal that Light-emitting Element 11 has lowdriving voltage and high current efficiency. It is thus confirmed that acompound to which one embodiment of the present invention is applied iseffective in realizing high voltage vs. luminance characteristics andhigh luminance vs. current efficiency characteristics.

As described above, by using PCPDBq produced in Example 11 as a hostmaterial of a light-emitting layer, a light-emitting element having lowdriving voltage and high current efficiency was able to be fabricated.

Example 20

In this example, a light-emitting element of one embodiment of thepresent invention will be described referring to FIG. 18. Chemicalformulae of materials used in this example are illustrated below. Notethat the chemical formulae of the materials which are illustrated aboveare omitted.

A method of fabricating Light-emitting Element 12 of this example willbe described below.

(Light-Emitting Element 12)

First, the first electrode 1101, the hole-injection layer 1111, and thehole-transport layer 1112 were formed over the glass substrate 1100 inthe same manner as those of Light-emitting Element 5 described inExample 13.

Next, 7-[3-(dibenzothiophen-4-yl)phenyl]dibenzo[f,h]quinoxaline(abbreviation: 7mDBTPDBq-II) (whose synthesis method is described inReference Example 3), PCBA1BP, and [Ir(mppr-Me)₂(acac)]) wereco-evaporated to form the light-emitting layer 1113 over thehole-transport layer 1112. The weight ratio of 7mDBTPDBq-II to PCBA1BPand [Ir(mppr-Me)₂(acac)] was adjusted to 1:0.15:0.06(=7mDBTPDBq-II:PCBA1BP:[Ir(mppr-Me)₂(acac)]). The thickness of thelight-emitting layer 1113 was set to 40 nm.

Further, a 7mDBTPDBq-II film was formed to a thickness of 10 nm over thelight-emitting layer 1113, whereby the first electron-transport layer1114 a was formed.

Then, a BPhen film was formed to a thickness of 20 nm over the firstelectron-transport layer 1114 a, whereby the second electron-transportlayer 1114 b was formed.

Further, a LiF film was formed to a thickness of 1 nm over the secondelectron-transport layer 1114 b by evaporation, whereby theelectron-injection layer 1115 was formed.

Lastly, an aluminum film was formed to a thickness of 200 nm byevaporation as the second electrode 1103 functioning as a cathode. Thus,Light-emitting Element 12 of this example was fabricated.

Note that, in the above evaporation process, evaporation was allperformed by a resistance heating method.

Table 17 shows an element structure of Light-emitting Element 12obtained as described above.

TABLE 17 First Second Hole- Hole- Light- electron- electron- Electron-First injection transport emitting transport transport injection Secondelectrode layer layer layer layer layer layer electrode Light- ITSOBPAFLP: BPAFLP 7mDBTPDBq- II: 7mDBTPDBq-II BPhen LiF Al emitting 110 nmMoOx 20 nm PCBA1BP: 10 nm 20 nm 1 nm 200 nm element 12 (=4:2)[Ir(mppr-Me)₂(acac)] 40 nm (=1:0.15:0.06) 40 nm

In a glove box containing a nitrogen atmosphere, Light-emitting Element12 was sealed with a glass substrate so as not to be exposed to air.Then, operation characteristics of the element were measured. Note thatthe measurements were carried out at room temperature (in the atmospherekept at 25° C.).

FIG. 62 shows the voltage vs. luminance characteristics ofLight-emitting Element 12. In FIG. 62, the horizontal axis representsvoltage (V) and the vertical axis represents luminance (cd/m²). Inaddition, FIG. 63 shows the luminance vs. current efficiencycharacteristics of the element. In FIG. 63, the horizontal axisrepresents luminance (cd/m²) and the vertical axis represents currentefficiency (cd/A). Further, Table 18 shows the voltage (V), currentdensity (mA/cm²), CIE chromaticity coordinates (x, y), currentefficiency (cd/A), and external quantum efficiency (%) of thelight-emitting element at a luminance of 720 cd/m².

TABLE 18 External Current Chroma- Chroma- Current quantum Voltagedensity ticity ticity Luminance efficiency efficiency (V) (mA/cm²) x y(cd/m²) (cd/A) (%) Light- 3.0 1.4 0.54 0.46 720 50 19 emitting element12

As shown in Table 18, the CIE chromaticity coordinates (x, y) ofLight-emitting Element 12 were (0.54, 0.46) at a luminance of 720 cd/m².It is found that Light-emitting Element 12 exhibited light emission from[Ir(mppr-Me)₂(acac)].

FIG. 62 and FIG. 63 reveal that Light-emitting Element 12 has lowdriving voltage and high current efficiency. It is thus confirmed that acompound to which one embodiment of the present invention is applied iseffective in realizing high voltage vs. luminance characteristics andhigh luminance vs. current efficiency characteristics.

As described above, by using 7mDBTPDBq-II as a host material of alight-emitting layer, a light-emitting element having low drivingvoltage and high current efficiency was able to be fabricated.

Example 21

In this example, a light-emitting element of one embodiment of thepresent invention will be described referring to FIG. 18. Chemicalformulae of materials used in this example are illustrated below. Notethat the chemical formulae of the materials which are illustrated aboveare omitted.

Methods of fabricating Light-emitting Element 13 and ReferenceLight-emitting Element 14 of this example will be described below.

(Light-Emitting Element 13)

First, the first electrode 1101, the hole-injection layer 1111, and thehole-transport layer 1112 were formed over the glass substrate 1100 inthe same manner as those of Light-emitting Element 5 described inExample 13.

Next, 2mDBTPDBq-II, PCBA1BP, and [Ir(mppr-Me)₂(acac)]) wereco-evaporated to form the light-emitting layer 1113 over thehole-transport layer 1112. The weight ratio of 2mDBTPDBq-II to PCBA1BPand [Ir(mppr-Me)₂(acac)] was adjusted to 1:0.25:0.06(=2mDBTPDBq-II:PCBA1BP:[Ir(mppr-Me)₂(acac)]). The thickness of thelight-emitting layer 1113 was set to 40 nm.

Further, a 2mDBTPDBq-II film was formed to a thickness of 10 nm over thelight-emitting layer 1113, whereby the first electron-transport layer1114 a was formed.

Then, a BPhen film was formed to a thickness of 20 nm over the firstelectron-transport layer 1114 a, whereby the second electron-transportlayer 1114 b was formed.

Further, a LiF film was formed to a thickness of 1 nm over the secondelectron-transport layer 1114 b by evaporation, whereby theelectron-injection layer 1115 was formed.

Lastly, an aluminum film was formed to a thickness of 200 nm byevaporation as the second electrode 1103 functioning as a cathode. Thus,Light-emitting Element 13 of this example was fabricated.

Note that, in the above evaporation process, evaporation was allperformed by a resistance heating method.

(Reference Light-Emitting Element 14)

The light-emitting layer 1113 of Reference Light-emitting Element 14 wasformed by co-evaporation of 2-phenyldibenzo[f,h]quinoxaline(abbreviation: 2PDBq), PCBA1BP, and [Ir(mppr-Me)₂(acac)]. The weightratio of 2PDBq to PCBA1BP and [Ir(mppr-Me)₂(acac)] was adjusted to1:0.25:0.06 (=2PDBq:PCBA1BP:[Ir(mppr-Me)₂(acac)]). The thickness of thelight-emitting layer 1113 was set to 40 nm.

The first electron-transport layer 1114 a of Reference Light-emittingElement 14 was formed with a 10-nm-thick 2PDBq film. The componentsother than the light-emitting layer 1113 and the firstelectron-transport layer 1114 a were formed in the same manner as thoseof Light-emitting Element 13.

Table 19 shows element structures of Light-emitting Element 13 andReference Light-emitting Element 14 obtained as described above.

TABLE 19 First Second Hole- Hole- Light- electron- electron- Electron-First injection transport emitting transport transport injection Secondelectrode layer layer layer layer layer layer electrode Light- ITSOBPAFLP: BPAFLP 2mDBTPDBq- II: 2mDBTPDBq-II BPhen LiF Al emitting 110 nmMoOx 20 nm PCBA1BP: 10 nm 20 nm 1 nm 200 nm element 13 (=4:2)[Ir(mppr-Me)₂(acac)] 40 nm (=1:0.25:0.06) 40 nm Reference ITSO BPAFLP:BPAFLP 2PDBq: 2PDBq BPhen LiF Al light- 110 nm MoOx 20 nm PCBA1BP: 10 nm20 nm 1 nm 200 nm emitting (=4:2) [Ir(mppr-Me)₂(acac)] element 14 40 nm(=1:0.25:0.06) 40 nm

In a glove box containing a nitrogen atmosphere, Light-emitting Element13 and Reference Light-emitting Element 14 were sealed with a glasssubstrate so as not to be exposed to air. Then, operationcharacteristics of these elements were measured. Note that themeasurements were carried out at room temperature (in the atmospherekept at 25° C.).

FIG. 64 shows the current density vs. luminance characteristics ofLight-emitting Element 13 and Reference Light-emitting Element 14. InFIG. 64, the horizontal axis represents current density (mA/cm²) and thevertical axis represents luminance (cd/m²). In addition, FIG. 65 showsthe voltage vs. luminance characteristics. In FIG. 65, the horizontalaxis represents voltage (V) and the vertical axis represents luminance(cd/m²). FIG. 66 shows the luminance vs. current efficiencycharacteristics. In FIG. 66, the horizontal axis represents luminance(cd/m²) and the vertical axis represents current efficiency (cd/A). FIG.67 shows the voltage vs. current characteristics. In FIG. 67, thehorizontal axis represents voltage (V) and the vertical axis representscurrent (mA). Further, Table 20 shows the voltage (V), current density(mA/cm²), CIE chromaticity coordinates (x, y), current efficiency(cd/A), and external quantum efficiency (%) of the light-emittingelement at a luminance of 1100 cd/m².

TABLE 20 External Current Chroma- Chroma- Current quantum Voltagedensity ticity ticity Luminance efficiency efficiency (V) (mA/cm²) x y(cd/m²) (cd/A) (%) Light- 3.4 2.2 0.54 0.45 1100 48 19 emitting element13 Reference 4.6 44 0.53 0.47 1100 2.4 0.9 light- emitting element 14

As shown in Table 20, the CIE chromaticity coordinates (x, y) ofLight-emitting Element 13 and Reference Light-emitting Element 14 wererespectively (0.54, 0.44) and (0.53, 0.47) at a luminance of 1100 cd/m².It is found that Light-emitting Element 13 and Reference Light-emittingElement 14 each exhibited light emission from [Ir(mppr-Me)₂(acac)].

FIG. 67 reveals that, in a region at voltage lower than the voltage (ofabout 2V) at which light emission starts, a larger current flows inReference Light-emitting Element 14 fabricated in this example than inLight-emitting Element 13. In addition, Table 20 indicates that thecurrent efficiency of Reference Light-emitting Element 14 issignificantly low. This is considered to be because 2PDBq used for thelight-emitting layer 1113 of Reference Light-emitting Element 14 iscrystallized and current leakage occurs.

In contrast, FIG. 64, FIG. 65, FIG. 66, and FIG. 67 demonstrate thatLight-emitting Element 13 has low driving voltage and high currentefficiency. It is thus confirmed that a compound to which one embodimentof the present invention is applied is effective in realizing highvoltage vs. luminance characteristics and high luminance vs. currentefficiency characteristics.

As described above, by using 2mDBTPDBq-II as a host material of alight-emitting layer, a light-emitting element having low drivingvoltage and high current efficiency was able to be fabricated.

Reference Example 1

A method of synthesizing4-phenyl-4′-(9-phenylfluoren-9-yl)triphenylamine (abbreviation: BPAFLP)used in Example 3 and the like above will be specifically described. Thestructure of BPAFLP is illustrated below.

Step 1: Synthesis Method of 9-(4-Bromophenyl)-9-phenylfluorene

In a 100-mL three-neck flask, 1.2 g (50 mmol) of magnesium was heatedand stirred under reduced pressure for 30 minutes, whereby the magnesiumwas activated. After the flask was cooled to room temperature and wasmade to have a nitrogen atmosphere, several drops of dibromoethane wereadded, so that foam formation and heat generation were confirmed. After12 g (50 mmol) of 2-bromobiphenyl dissolved in 10 mL of diethyl etherwas slowly dripped into this mixture, the mixture was stirred and heatedunder reflux for 2.5 hours, whereby a Grignard reagent was prepared.

In a 500-mL three-neck flask were put 10 g (40 mmol) of4-bromobenzophenone and 100 mL of diethyl ether. After the Grignardreagent prepared as above was slowly dripped into this mixture, themixture was heated and stirred under reflux for 9 hours.

After reaction, this mixed liquid was filtered to give a substance. Thesubstance obtained by the filtration was dissolved in 150 mL of ethylacetate, and 1N-hydrochloric acid was added to the mixture, which wasthen stirred for 2 hours until it was made acid. The organic layer ofthis liquid was washed with water. Then, magnesium sulfate was addedthereto so that moisture is removed. This suspension was filtered, andthe resulting filtrate was concentrated to give a highly viscous liquid.

In a 500-mL recovery flask were put this highly viscous liquid, 50 mL ofglacial acetic acid, and 1.0 mL of hydrochloric acid. The mixture washeated and stirred under a nitrogen atmosphere at 130° C. for 1.5 hoursto be reacted.

After reaction, this reaction mixed liquid was filtered to give asubstance. The substance obtained by the filtration was washed withwater, an aqueous sodium hydroxide solution, water, and methanol in thisorder. Then, the mixture was dried to give 11 g of a white powder in 69%yield, which was the substance to be produced. The reaction scheme ofthe synthesis method is illustrated in the following (D−1).

Step 2: Synthesis Method of4-Phenyl-4′-(9-phenylfluoren-9-yl)triphenylamine (abbreviation: BPAFLP)

In a 100-mL three-neck flask were put 3.2 g (8.0 mmol) of9-(4-bromophenyl)-9-phenylfluorene, 2.0 g (8.0 mmol) of4-phenyl-diphenylamine, 1.0 g (10 mmol) of sodium tert-butoxide, and 23mg (0.04 mmol) of bis(dibenzylideneacetone)palladium(0). The air in theflask was replaced with nitrogen. Then, 20 mL of dehydrated xylene wasadded to this mixture. After the mixture was degassed by stirring underreduced pressure, 0.2 mL (0.1 mmol) of tri(tert-butyl)phosphine (a 10 wt% hexane solution) was added to the mixture. This mixture was heated andstirred under a nitrogen atmosphere at 110° C. for 2 hours to bereacted.

After reaction, 200 mL of toluene was added to the reaction mixedliquid, and this suspension was filtered through Florisil (produced byWako Pure Chemical Industries, Ltd., Catalog No. 540-00135) and Celite(produced by Wako Pure Chemical Industries, Ltd., Catalog No.531-16855). The filtrate was concentrated, and the resulting substancewas purified by silica gel column chromatography (with a developingsolvent of toluene and hexane in a ratio of 1:4). The obtained fractionswere concentrated, and acetone and methanol were added to the mixture.The mixture was irradiated with ultrasonic waves and then recrystallizedto give 4.1 g of a white powder in 92% yield, which was the substance tobe produced. The reaction scheme of the synthesis method is illustratedin the following (D-2).

The Rf values of the produced substance,9-(4-bromophenyl)-9-phenylfluorene, and 4-phenyl-diphenylamine wererespectively 0.41, 0.51, and 0.27, which were found by silica gel thinlayer chromatography (TLC) (with a developing solvent of ethyl acetateand hexane in a ratio of 1:10).

The compound obtained through the above Step 2 was subjected to anuclear magnetic resonance (NMR) method. The measurement data are shownbelow. The measurement results indicate that the obtained compound wasBPAFLP, which is a fluorene derivative.

¹H NMR (CDCl₃, 300 MHz): δ (ppm)=6.63-7.02 (m, 3H), 7.06-7.11 (m, 6H),7.19-7.45 (m, 18H), 7.53-7.55 (m, 2H), 7.75 (d, J=6.9 Hz, 2H).

Reference Example 2

A method of synthesizing(dipivaloylmethanato)bis(3,5-dimethyl-2-phenylpyrazinato)iridium(III)(abbreviation: [Ir(mppr-Me)₂(dpm)]) used in Example 13 and the likeabove will be specifically described. The structure of[Ir(mppr-Me)₂(dpm)] is illustrated below.

First, 20 mL of 2-ethoxyethanol, 1.55 g of a binuclear complexdi-μ-chloro-bis[bis(3,5-dimethyl-2-phenylpyrazinato)iridium(III)](abbreviation: [Ir(mppr-Me)₂Cl]₂), 0.8 ml of dipivaloylmethane, and 1.38g of sodium carbonate were mixed. The mixture was irradiated withmicrowaves under argon bubbling for 30 minutes, whereby the mixture wasreacted. After reaction, the reaction solution was cooled down to roomtemperature, and water was added thereto. This mixture solution wasseparated into an organic layer and an aqueous layer, and organicsubstances were extracted from the aqueous layer with dichloromethane.The organic layer was combined with the solution of the extractedorganic substances, the mixture was washed with water, followed bydrying with anhydrous magnesium sulfate. After that, the mixture wasgravity filtered, and the filtrate was concentrated to dry and harden.This solid was recrystallized from a mixed solvent of dichloromethaneand ethanol to give a red powder in a yield of 67%. Note that theirradiation with microwaves was performed using a microwave synthesissystem (Discover, manufactured by CEM Corporation). The synthesis schemeof this step is illustrate in the following (E-1).

Note that a nuclear magnetic resonance (¹H NMR) method identified thiscompound as an organometallic complex [Ir(mppr-Me)₂(dpm)], which was thesubstance to be produced. The obtained ¹H NMR analysis results are shownbelow.

¹H NMR. δ (CDCl₃): 0.90 (s, 1H), 2.59 (s, 6H), 3.04 (s, 6H), 5.49 (s,1H), 6.32 (dd, 2H), 6.70 (dt, 2H), 6.88 (dt, 2H), 7.86 (d, 2H), 8.19 (s,2H).

Reference Example 3

A method of synthesizing7-[3-(dibenzothiophen-4-yl)phenyl]dibenzo[f,h]quinoxaline (abbreviation:7mDBTPDBq-II) used in Example 20 and the like will be specificallydescribed. The structure of 7mDBTPDBq-II is illustrated below.

[Synthesis of 7mDBTPDBq-II]

A scheme for the synthesis of 7mDBTPDBq-II is illustrated in (F-1).

In a 50-mL three-neck flask were put 1.2 g (4.0 mmol) of7-bromodibenzo[f,h]quinoxaline, 1.3 g (4.3 mmol) of3-(dibenzothiophen-4-yl)phenylboronic acid, 20 mL of toluene, 4 mL ofethanol, and 4 mL of a 2M aqueous potassium carbonate solution. Thismixture was degassed by stirring under reduced pressure. To this mixturewas added 93 mg (81 μmol) of tetrakis(triphenylphosphine)palladium(0).This mixture was stirred under a nitrogen stream at 80° C. for 7 hours.After a predetermined time had elapsed, water was added to the obtainedmixture, organic substances were extracted from the aqueous layer withtoluene. The obtained solution of the extracted organic substances wascombined with the organic layer, the mixture was washed with water andsaturated brine, and the organic layer was dried with magnesium sulfate.This mixture was gravity filtered, and the filtrate was concentrated togive a solid. The obtained solid was purified by silica gel columnchromatography (with a developing solvent of toluene) and recrystallizedfrom toluene to give 1.4 g of a pale yellow powder in 61% yield, whichwas the substance to be produced.

By a train sublimation method, 1.4 g of the obtained pale yellow powder,which was the produced substance, was purified. In the purification, theproduced substance was heated at 255° C. under a pressure of 2.5 Pa witha flow rate of argon gas of 5 mL/min. After the purification, 0.60 g ofa pale yellow powder was obtained in a yield of 42%, which was thesubstance to be produced.

¹H NMR data of the obtained substance are as follows: ¹H NMR (CDCl₃, 300MHz): δ=7.47-7.51 (m, 2H), 7.62 (d, J=4.8 Hz, 2H), 7.68-7.92 (m, 6H),8.08 (dd, J=8.4 Hz, 1.5 Hz, 1H), 8.19-8.24 (m, 3H), 8.74 (dd, J=7.8 Hz,1.5 Hz, 1H), 8.91-8.93 (m, 3H), 9.24 (dd, J=7.2 Hz, 2.1 Hz, 1H), 9.31(d, J=8.4 Hz, 1H).

This application is based on Japanese Patent Application serial no.2010-044720 filed with the Japan Patent Office on Mar. 1, 2010, theentire contents of which are hereby incorporated by reference.

What is claimed is:
 1. A light-emitting device comprising: alight-emitting element comprising a light-emitting layer comprising: alight-emitting material; and a compound comprising adibenzo[f,h]quinoxaline ring and a hole-transport skeleton which arebonded to each other through an arylene group, wherein thehole-transport skeleton is a carbazole ring, and wherein the compound isa host material.
 2. The light-emitting device according to claim 1,wherein the arylene group comprises one or more substituents.
 3. Thelight-emitting device according to claim 2, wherein the substituents arebonded to form a ring.
 4. The light-emitting device according to claim1, wherein the arylene group is any of a substituted or unsubstitutedphenylene group, a substituted or unsubstituted biphenyldiyl group, anda substituted or unsubstituted m-phenylene group.
 5. The light-emittingdevice according to claim 1, wherein the light-emitting elementcomprises an electron-transport layer, and wherein theelectron-transport layer comprises the compound.
 6. A light-emittingdevice comprising: a light-emitting element comprising: a light-emittinglayer comprising a light-emitting material; and an electron-transportlayer comprising a compound represented by General Formula (G1):

wherein A represents a substituted or unsubstituted carbazolyl group,wherein R¹¹ to R¹⁹ independently represent any of hydrogen, an alkylgroup having 1 to 4 carbon atoms, and a substituted or unsubstitutedaryl group having 6 to 13 carbon atoms, and wherein Ar represents anarylene group having 6 to 13 carbon atoms.
 7. The light-emitting deviceaccording to claim 6, wherein the arylene group comprises one or moresubstituents.
 8. The light-emitting device according to claim 7, whereinthe substituents are bonded to form a ring.
 9. The light-emitting deviceaccording to claim 6, wherein Ar is any of a substituted orunsubstituted phenylene group, a substituted or unsubstitutedbiphenyldiyl group, and a substituted or unsubstituted m-phenylenegroup.
 10. The light-emitting device according to claim 6, wherein thecompound is represented by General Formula (G2-2),

wherein R³¹ to R³⁸ independently represent hydrogen, an alkyl grouphaving 1 to 4 carbon atoms, or a substituted or unsubstituted aryl grouphaving 6 to 13 carbon atoms.
 11. The light-emitting device according toclaim 10, wherein the arylene group has one or more substituents. 12.The light-emitting device according to claim 11, wherein thesubstituents are bonded to form a ring.
 13. The light-emitting deviceaccording to claim 10, wherein Ar is any of a substituted orunsubstituted phenylene group, a substituted or unsubstitutedbiphenyldiyl group, and a substituted or unsubstituted m-phenylenegroup.
 14. The light-emitting device according to claim 10, wherein Aris one represented by formulae (1-1) to (1-15),


15. The light-emitting device according to claim 10, wherein thecompound is represented by General Formula (G3-2),

wherein R⁴¹ to R⁴⁴ independently represent hydrogen, an alkyl grouphaving 1 to 4 carbon atoms, or a substituted or unsubstituted aryl grouphaving 6 to 13 carbon atoms.
 16. The light-emitting device according toclaim 15, wherein R⁴² and R⁴³ are bonded to R⁴³ and R⁴⁴ respectively toform a ring.
 17. The light-emitting device according to claim 15,wherein R¹¹ to R¹⁹, R³¹ to R³⁸, and R⁴¹ to R⁴⁴ independently representone represented by formulae (2-1) to (2-23),


18. The light-emitting device according to claim 15, wherein thecompound is one represented by formulae (309), (326), and (338),


19. The light-emitting device according to claim 15, wherein thecompound is one represented by formulae (318) to (322),


20. The light-emitting device according to claim 15, wherein thecompound is represented by formula (400),


21. The light-emitting device according to claim 15, wherein thecompound is one represented by formulae (401), (402), (406), (408), and(470),


22. A light-emitting device comprising: a light-emitting elementcomprising a light-emitting layer comprising: a light-emitting material;and a compound represented by General Formula (G1):

wherein A represents a substituted or unsubstituted carbazolyl group,wherein R¹¹ to R¹⁹ independently represent any of hydrogen, an alkylgroup having 1 to 4 carbon atoms, and a substituted or unsubstitutedaryl group having 6 to 13 carbon atoms, and wherein Ar represents anarylene group having 6 to 13 carbon atoms.
 23. The light-emitting deviceaccording to claim 1, wherein the compound is represented by GeneralFormula (G1):

wherein A represents a substituted or unsubstituted carbazolyl group,wherein R¹¹ to R¹⁹ independently represent any of hydrogen, an alkylgroup having 1 to 4 carbon atoms, and a substituted or unsubstitutedaryl group having 6 to 13 carbon atoms, and wherein Ar represents anarylene group having 6 to 13 carbon atoms.
 24. The light-emitting deviceaccording to claim 23, wherein the compound is represented by GeneralFormula (G2-2),

wherein R³¹ to R³⁸ independently represent hydrogen, an alkyl grouphaving 1 to 4 carbon atoms, or a substituted or unsubstituted aryl grouphaving 6 to 13 carbon atoms.
 25. The light-emitting device according toclaim 23, wherein Ar is one represented by formulae (1-1) to (1-15),


26. The light-emitting device according to claim 23, wherein thecompound is represented by General Formula (G3-2),

wherein R⁴¹ to R⁴⁴ independently represent hydrogen, an alkyl grouphaving 1 to 4 carbon atoms, or a substituted or unsubstituted aryl grouphaving 6 to 13 carbon atoms.
 27. The light-emitting device according toclaim 26, wherein R¹¹ to R¹⁹, R³¹ to R³⁸, and R⁴¹ to R⁴⁴ independentlyrepresent one represented by formulae (2-1) to (2-23),


28. The light-emitting device according to claim 1, wherein the compoundis one represented by formulae (309), (326), and (338),


29. The light-emitting device according to claim 1, wherein the compoundis one represented by formulae (318) to (322),


30. The light-emitting device according to claim 1, wherein the compoundis represented by formula (400),


31. The light-emitting device according to claim 22, wherein thecompound is represented by General Formula (G2-2),

wherein R³¹ to R³⁸ independently represent hydrogen, an alkyl grouphaving 1 to 4 carbon atoms, or a substituted or unsubstituted aryl grouphaving 6 to 13 carbon atoms.
 32. The light-emitting device according toclaim 22, wherein Ar is one represented by formulae (1-1) to (1-15),


33. The light-emitting device according to claim 22, wherein thecompound is represented by General Formula (G3-2),

wherein R⁴¹ to R⁴⁴ independently represent hydrogen, an alkyl grouphaving 1 to 4 carbon atoms, or a substituted or unsubstituted aryl grouphaving 6 to 13 carbon atoms.
 34. The light-emitting device according toclaim 33, wherein R¹¹ to R¹⁹, R³¹ to R³⁸, and R⁴¹ to R⁴⁴ independentlyrepresent one represented by formulae (2-1) to (2-23),


35. The light-emitting device according to claim 22, wherein thecompound is one represented by formulae (309), (326), and (338),


36. The light-emitting device according to claim 22, wherein thecompound is one represented by formulae (318) to (322),


37. The light-emitting device according to claim 22, wherein thecompound is represented by formula (400),